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 $84.90   9.767%   $93.1922   $93.19   $93.20   $93.20  
  Purchase #2 $57.62   9.517%   $63.1037   $63.10   $63.10   $63.10  
  Purchase #3 $197.38   8.811%   $214.7712   $214.77   $214.75   $214.80  
  Purchase #4 $33.67   11.830%   $37.6532   $37.65   $37.65   $37.70  
  Purchase #5 $222.26   3.281%   $229.5524   $229.55   $229.55   $229.60  
  Purchase #6 $39.92   12.606%   $44.9523   $44.95   $44.95   $45.00  
  Purchase #7 $244.32   3.267%   $252.3019   $252.30   $252.30   $252.30  
  7 purchase totals = $880.07       $935.5269   $935.51   $935.50   $935.70