Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.25   13.710%   $267.5028   $267.50   $267.50   $267.50  
  Purchase #2 $156.52   10.836%   $173.4805   $173.48   $173.50   $173.50  
  Purchase #3 $238.79   3.141%   $246.2904   $246.29   $246.30   $246.30  
  Purchase #4 $113.45   12.762%   $127.9285   $127.93   $127.95   $127.90  
  Purchase #5 $151.60   6.656%   $161.6905   $161.69   $161.70   $161.70  
  Purchase #6 $237.79   13.134%   $269.0213   $269.02   $269.00   $269.00  
  Purchase #7 $91.36   12.453%   $102.7371   $102.74   $102.75   $102.70  
  7 purchase totals = $1,224.76       $1,348.6511   $1,348.65   $1,348.70   $1,348.60