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 $232.97   12.766%   $262.711   $262.71   $262.70   $262.70  
  Purchase #2 $13.82   3.320%   $14.2788   $14.28   $14.30   $14.30  
  Purchase #3 $97.63   6.221%   $103.7036   $103.70   $103.70   $103.70  
  Purchase #4 $68.60   7.310%   $73.6147   $73.61   $73.60   $73.60  
  Purchase #5 $236.83   13.298%   $268.3237   $268.32   $268.30   $268.30  
  Purchase #6 $191.62   5.518%   $202.1936   $202.19   $202.20   $202.20  
  Purchase #7 $32.43   3.245%   $33.4824   $33.48   $33.50   $33.50  
  7 purchase totals = $873.90       $958.3078   $958.29   $958.30   $958.30