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 $87.32   6.233%   $92.7627   $92.76   $92.75   $92.80  
  Purchase #2 $25.58   13.416%   $29.0118   $29.01   $29.00   $29.00  
  Purchase #3 $53.66   7.663%   $57.772   $57.77   $57.75   $57.80  
  Purchase #4 $113.93   5.154%   $119.802   $119.80   $119.80   $119.80  
  Purchase #5 $167.47   12.640%   $188.6382   $188.64   $188.65   $188.60  
  Purchase #6 $125.48   3.703%   $130.1265   $130.13   $130.15   $130.10  
  Purchase #7 $144.68   4.650%   $151.4076   $151.41   $151.40   $151.40  
  7 purchase totals = $718.12       $769.5208   $769.52   $769.50   $769.50