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 $110.45   6.851%   $118.0169   $118.02   $118.00   $118.00  
  Purchase #2 $167.32   10.266%   $184.4971   $184.50   $184.50   $184.50  
  Purchase #3 $105.38   12.344%   $118.3881   $118.39   $118.40   $118.40  
  Purchase #4 $75.78   4.856%   $79.4599   $79.46   $79.45   $79.50  
  Purchase #5 $16.68   11.638%   $18.6212   $18.62   $18.60   $18.60  
  Purchase #6 $17.36   11.858%   $19.4185   $19.42   $19.40   $19.40  
  Purchase #7 $246.75   3.134%   $254.4831   $254.48   $254.50   $254.50  
  7 purchase totals = $739.72       $792.8848   $792.89   $792.85   $792.90