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 $165.76   12.669%   $186.7601   $186.76   $186.75   $186.80  
  Purchase #2 $148.28   12.600%   $166.9633   $166.96   $166.95   $167.00  
  Purchase #3 $227.71   5.851%   $241.0333   $241.03   $241.05   $241.00  
  Purchase #4 $162.87   10.790%   $180.4437   $180.44   $180.45   $180.40  
  Purchase #5 $243.84   6.864%   $260.5772   $260.58   $260.60   $260.60  
  Purchase #6 $218.30   13.533%   $247.8425   $247.84   $247.85   $247.80  
  Purchase #7 $190.53   11.804%   $213.0202   $213.02   $213.00   $213.00  
  7 purchase totals = $1,357.29       $1,496.6403   $1,496.63   $1,496.65   $1,496.60