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 $31.92   12.826%   $36.0141   $36.01   $36.00   $36.00  
  Purchase #2 $207.97   6.766%   $222.0413   $222.04   $222.05   $222.00  
  Purchase #3 $173.92   9.567%   $190.5589   $190.56   $190.55   $190.60  
  Purchase #4 $125.82   7.274%   $134.9721   $134.97   $134.95   $135.00  
  Purchase #5 $85.92   4.164%   $89.4977   $89.50   $89.50   $89.50  
  Purchase #6 $32.94   3.665%   $34.1473   $34.15   $34.15   $34.10  
  Purchase #7 $247.56   4.168%   $257.8783   $257.88   $257.90   $257.90  
  7 purchase totals = $906.05       $965.1097   $965.11   $965.10   $965.10