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 $243.33   10.123%   $267.9623   $267.96   $267.95   $268.00  
  Purchase #2 $29.93   10.772%   $33.1541   $33.15   $33.15   $33.20  
  Purchase #3 $9.86   6.301%   $10.4813   $10.48   $10.50   $10.50  
  Purchase #4 $105.92   3.388%   $109.5086   $109.51   $109.50   $109.50  
  Purchase #5 $189.45   6.739%   $202.217   $202.22   $202.20   $202.20  
  Purchase #6 $74.54   9.587%   $81.6861   $81.69   $81.70   $81.70  
  Purchase #7 $206.99   3.148%   $213.506   $213.51   $213.50   $213.50  
  7 purchase totals = $860.02       $918.5154   $918.52   $918.50   $918.60