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 $117.53   7.221%   $126.0168   $126.02   $126.00   $126.00  
  Purchase #2 $193.63   9.711%   $212.4334   $212.43   $212.45   $212.40  
  Purchase #3 $25.62   10.172%   $28.2261   $28.23   $28.25   $28.20  
  Purchase #4 $133.67   12.685%   $150.626   $150.63   $150.65   $150.60  
  Purchase #5 $85.62   10.648%   $94.7368   $94.74   $94.75   $94.70  
  Purchase #6 $242.57   10.847%   $268.8816   $268.88   $268.90   $268.90  
  Purchase #7 $89.60   5.481%   $94.511   $94.51   $94.50   $94.50  
  7 purchase totals = $888.24       $975.4317   $975.44   $975.50   $975.30