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 $30.89   8.550%   $33.5311   $33.53   $33.55   $33.50  
  Purchase #2 $116.82   10.202%   $128.738   $128.74   $128.75   $128.70  
  Purchase #3 $59.42   11.808%   $66.4363   $66.44   $66.45   $66.40  
  Purchase #4 $66.67   8.371%   $72.2509   $72.25   $72.25   $72.30  
  Purchase #5 $93.93   10.819%   $104.0923   $104.09   $104.10   $104.10  
  Purchase #6 $71.60   4.186%   $74.5972   $74.60   $74.60   $74.60  
  Purchase #7 $106.59   7.676%   $114.7718   $114.77   $114.75   $114.80  
  7 purchase totals = $545.92       $594.4176   $594.42   $594.45   $594.40