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 $153.61   6.462%   $163.5363   $163.54   $163.55   $163.50  
  Purchase #2 $181.87   11.148%   $202.1449   $202.14   $202.15   $202.10  
  Purchase #3 $60.52   11.651%   $67.5712   $67.57   $67.55   $67.60  
  Purchase #4 $214.48   10.247%   $236.4578   $236.46   $236.45   $236.50  
  Purchase #5 $182.73   12.703%   $205.9422   $205.94   $205.95   $205.90  
  Purchase #6 $35.62   10.629%   $39.406   $39.41   $39.40   $39.40  
  Purchase #7 $38.36   6.747%   $40.9481   $40.95   $40.95   $40.90  
  7 purchase totals = $867.19       $956.0065   $956.01   $956.00   $955.90