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 $30.93   5.711%   $32.6964   $32.70   $32.70   $32.70  
  Purchase #2 $184.51   11.391%   $205.5275   $205.53   $205.55   $205.50  
  Purchase #3 $110.87   9.842%   $121.7818   $121.78   $121.80   $121.80  
  Purchase #4 $92.76   9.628%   $101.6909   $101.69   $101.70   $101.70  
  Purchase #5 $63.58   7.606%   $68.4159   $68.42   $68.40   $68.40  
  Purchase #6 $112.59   13.429%   $127.7097   $127.71   $127.70   $127.70  
  Purchase #7 $71.60   7.397%   $76.8963   $76.90   $76.90   $76.90  
  7 purchase totals = $666.84       $734.7185   $734.73   $734.75   $734.70