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 $222.25   7.549%   $239.0277   $239.03   $239.05   $239.00  
  Purchase #2 $198.88   12.607%   $223.9528   $223.95   $223.95   $224.00  
  Purchase #3 $85.38   3.763%   $88.5928   $88.59   $88.60   $88.60  
  Purchase #4 $14.34   8.714%   $15.5896   $15.59   $15.60   $15.60  
  Purchase #5 $133.36   9.148%   $145.5598   $145.56   $145.55   $145.60  
  Purchase #6 $247.29   5.232%   $260.2282   $260.23   $260.25   $260.20  
  Purchase #7 $21.46   3.105%   $22.1263   $22.13   $22.15   $22.10  
  7 purchase totals = $922.96       $995.0772   $995.08   $995.15   $995.10