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 $215.28   13.663%   $244.6937   $244.69   $244.70   $244.70  
  Purchase #2 $41.72   6.143%   $44.2829   $44.28   $44.30   $44.30  
  Purchase #3 $224.29   11.266%   $249.5585   $249.56   $249.55   $249.60  
  Purchase #4 $119.62   3.312%   $123.5818   $123.58   $123.60   $123.60  
  Purchase #5 $192.82   10.170%   $212.4298   $212.43   $212.45   $212.40  
  Purchase #6 $58.67   8.190%   $63.4751   $63.48   $63.50   $63.50  
  Purchase #7 $181.68   10.477%   $200.7146   $200.71   $200.70   $200.70  
  7 purchase totals = $1,034.08       $1,138.7364   $1,138.73   $1,138.80   $1,138.80