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 $231.46   9.624%   $253.7357   $253.74   $253.75   $253.70  
  Purchase #2 $236.48   4.513%   $247.1523   $247.15   $247.15   $247.20  
  Purchase #3 $154.61   4.316%   $161.283   $161.28   $161.30   $161.30  
  Purchase #4 $94.36   3.310%   $97.4833   $97.48   $97.50   $97.50  
  Purchase #5 $248.76   9.347%   $272.0116   $272.01   $272.00   $272.00  
  Purchase #6 $38.27   13.308%   $43.363   $43.36   $43.35   $43.40  
  Purchase #7 $121.41   11.778%   $135.7097   $135.71   $135.70   $135.70  
  7 purchase totals = $1,125.35       $1,210.7386   $1,210.73   $1,210.75   $1,210.80