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 $88.79   10.403%   $98.0268   $98.03   $98.05   $98.00  
  Purchase #2 $244.84   13.620%   $278.1872   $278.19   $278.20   $278.20  
  Purchase #3 $228.82   5.176%   $240.6637   $240.66   $240.65   $240.70  
  Purchase #4 $98.81   3.364%   $102.134   $102.13   $102.15   $102.10  
  Purchase #5 $192.46   3.869%   $199.9063   $199.91   $199.90   $199.90  
  Purchase #6 $120.71   12.663%   $135.9955   $136.00   $136.00   $136.00  
  Purchase #7 $157.47   5.628%   $166.3324   $166.33   $166.35   $166.30  
  7 purchase totals = $1,131.90       $1,221.2459   $1,221.25   $1,221.30   $1,221.20