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 $48.95   9.192%   $53.4495   $53.45   $53.45   $53.40  
  Purchase #2 $187.61   9.368%   $205.1853   $205.19   $205.20   $205.20  
  Purchase #3 $146.49   13.713%   $166.5782   $166.58   $166.60   $166.60  
  Purchase #4 $53.26   13.619%   $60.5135   $60.51   $60.50   $60.50  
  Purchase #5 $91.25   3.165%   $94.1381   $94.14   $94.15   $94.10  
  Purchase #6 $209.51   4.714%   $219.3863   $219.39   $219.40   $219.40  
  Purchase #7 $112.35   4.729%   $117.663   $117.66   $117.65   $117.70  
  7 purchase totals = $849.42       $916.9139   $916.92   $916.95   $916.90