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 $204.39   8.862%   $222.503   $222.50   $222.50   $222.50  
  Purchase #2 $58.90   6.192%   $62.5471   $62.55   $62.55   $62.50  
  Purchase #3 $79.86   9.812%   $87.6959   $87.70   $87.70   $87.70  
  Purchase #4 $225.32   8.756%   $245.049   $245.05   $245.05   $245.00  
  Purchase #5 $193.51   12.213%   $217.1434   $217.14   $217.15   $217.10  
  Purchase #6 $7.63   6.296%   $8.1104   $8.11   $8.10   $8.10  
  Purchase #7 $156.94   7.447%   $168.6273   $168.63   $168.65   $168.60  
  7 purchase totals = $926.55       $1,011.6761   $1,011.68   $1,011.70   $1,011.50