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 $87.49   6.252%   $92.9599   $92.96   $92.95   $93.00  
  Purchase #2 $104.54   5.851%   $110.6566   $110.66   $110.65   $110.70  
  Purchase #3 $111.84   9.517%   $122.4838   $122.48   $122.50   $122.50  
  Purchase #4 $7.56   5.113%   $7.9465   $7.95   $7.95   $7.90  
  Purchase #5 $223.85   10.517%   $247.3923   $247.39   $247.40   $247.40  
  Purchase #6 $216.86   8.709%   $235.7463   $235.75   $235.75   $235.70  
  Purchase #7 $30.36   12.642%   $34.1981   $34.20   $34.20   $34.20  
  7 purchase totals = $782.50       $851.3835   $851.39   $851.40   $851.40