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 $83.35   11.548%   $92.9753   $92.98   $93.00   $93.00  
  Purchase #2 $209.51   3.556%   $216.9602   $216.96   $216.95   $217.00  
  Purchase #3 $110.69   4.595%   $115.7762   $115.78   $115.80   $115.80  
  Purchase #4 $190.47   7.492%   $204.74   $204.74   $204.75   $204.70  
  Purchase #5 $75.43   12.639%   $84.9636   $84.96   $84.95   $85.00  
  Purchase #6 $29.62   10.859%   $32.8364   $32.84   $32.85   $32.80  
  Purchase #7 $127.84   5.246%   $134.5465   $134.55   $134.55   $134.50  
  7 purchase totals = $826.91       $882.7982   $882.81   $882.85   $882.80