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 $61.58   7.193%   $66.0094   $66.01   $66.00   $66.00  
  Purchase #2 $114.81   3.309%   $118.6091   $118.61   $118.60   $118.60  
  Purchase #3 $199.94   8.840%   $217.6147   $217.61   $217.60   $217.60  
  Purchase #4 $68.88   9.772%   $75.611   $75.61   $75.60   $75.60  
  Purchase #5 $75.62   6.450%   $80.4975   $80.50   $80.50   $80.50  
  Purchase #6 $220.39   5.175%   $231.7952   $231.80   $231.80   $231.80  
  Purchase #7 $155.31   7.299%   $166.6461   $166.65   $166.65   $166.60  
  7 purchase totals = $896.53       $956.7830   $956.79   $956.75   $956.70