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 $57.25   12.161%   $64.2122   $64.21   $64.20   $64.20  
  Purchase #2 $250.43   11.693%   $279.7128   $279.71   $279.70   $279.70  
  Purchase #3 $26.69   13.231%   $30.2214   $30.22   $30.20   $30.20  
  Purchase #4 $44.31   8.132%   $47.9133   $47.91   $47.90   $47.90  
  Purchase #5 $191.40   11.376%   $213.1737   $213.17   $213.15   $213.20  
  Purchase #6 $235.29   6.241%   $249.9744   $249.97   $249.95   $250.00  
  Purchase #7 $245.61   8.701%   $266.9805   $266.98   $267.00   $267.00  
  7 purchase totals = $1,050.98       $1,152.1883   $1,152.17   $1,152.10   $1,152.20