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 $111.40   12.359%   $125.1679   $125.17   $125.15   $125.20  
  Purchase #2 $206.93   13.170%   $234.1827   $234.18   $234.20   $234.20  
  Purchase #3 $121.88   3.819%   $126.5346   $126.53   $126.55   $126.50  
  Purchase #4 $72.89   9.155%   $79.5631   $79.56   $79.55   $79.60  
  Purchase #5 $244.52   8.277%   $264.7589   $264.76   $264.75   $264.80  
  Purchase #6 $42.56   4.315%   $44.3965   $44.40   $44.40   $44.40  
  Purchase #7 $210.74   4.176%   $219.5405   $219.54   $219.55   $219.50  
  7 purchase totals = $1,010.92       $1,094.1442   $1,094.14   $1,094.15   $1,094.20