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 $225.71   13.728%   $256.6955   $256.70   $256.70   $256.70  
  Purchase #2 $222.73   7.464%   $239.3546   $239.35   $239.35   $239.40  
  Purchase #3 $54.72   13.566%   $62.1433   $62.14   $62.15   $62.10  
  Purchase #4 $243.67   10.206%   $268.539   $268.54   $268.55   $268.50  
  Purchase #5 $10.76   6.866%   $11.4988   $11.50   $11.50   $11.50  
  Purchase #6 $216.98   12.162%   $243.3691   $243.37   $243.35   $243.40  
  Purchase #7 $70.41   10.188%   $77.5834   $77.58   $77.60   $77.60  
  7 purchase totals = $1,044.98       $1,159.1837   $1,159.18   $1,159.20   $1,159.20