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 $56.28   11.512%   $62.759   $62.76   $62.75   $62.80  
  Purchase #2 $200.91   12.542%   $226.1081   $226.11   $226.10   $226.10  
  Purchase #3 $210.93   6.624%   $224.902   $224.90   $224.90   $224.90  
  Purchase #4 $68.71   13.468%   $77.9639   $77.96   $77.95   $78.00  
  Purchase #5 $172.43   7.750%   $185.7933   $185.79   $185.80   $185.80  
  Purchase #6 $52.55   11.535%   $58.6116   $58.61   $58.60   $58.60  
  Purchase #7 $83.32   5.836%   $88.1826   $88.18   $88.20   $88.20  
  7 purchase totals = $845.13       $924.3205   $924.31   $924.30   $924.40