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 $54.42   10.524%   $60.1472   $60.15   $60.15   $60.10  
  Purchase #2 $106.33   12.356%   $119.4681   $119.47   $119.45   $119.50  
  Purchase #3 $145.74   8.843%   $158.6278   $158.63   $158.65   $158.60  
  Purchase #4 $111.95   10.538%   $123.7473   $123.75   $123.75   $123.70  
  Purchase #5 $205.93   11.194%   $228.9818   $228.98   $229.00   $229.00  
  Purchase #6 $111.67   6.161%   $118.55   $118.55   $118.55   $118.60  
  Purchase #7 $146.61   5.824%   $155.1486   $155.15   $155.15   $155.10  
  7 purchase totals = $882.65       $964.6708   $964.68   $964.70   $964.60