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 $68.42   7.590%   $73.6131   $73.61   $73.60   $73.60  
  Purchase #2 $197.80   7.593%   $212.819   $212.82   $212.80   $212.80  
  Purchase #3 $180.37   12.273%   $202.5068   $202.51   $202.50   $202.50  
  Purchase #4 $34.72   11.535%   $38.725   $38.73   $38.75   $38.70  
  Purchase #5 $71.40   3.175%   $73.667   $73.67   $73.65   $73.70  
  Purchase #6 $139.66   7.613%   $150.2923   $150.29   $150.30   $150.30  
  Purchase #7 $143.37   7.136%   $153.6009   $153.60   $153.60   $153.60  
  7 purchase totals = $835.74       $905.2241   $905.23   $905.20   $905.20