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 $64.45   11.265%   $71.7103   $71.71   $71.70   $71.70  
  Purchase #2 $219.53   10.658%   $242.9275   $242.93   $242.95   $242.90  
  Purchase #3 $8.48   6.585%   $9.0384   $9.04   $9.05   $9.00  
  Purchase #4 $150.25   8.116%   $162.4443   $162.44   $162.45   $162.40  
  Purchase #5 $15.57   8.611%   $16.9107   $16.91   $16.90   $16.90  
  Purchase #6 $207.51   8.419%   $224.9803   $224.98   $225.00   $225.00  
  Purchase #7 $225.69   10.753%   $249.9584   $249.96   $249.95   $250.00  
  7 purchase totals = $891.48       $977.9699   $977.97   $978.00   $977.90