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 $118.61   4.804%   $124.308   $124.31   $124.30   $124.30  
  Purchase #2 $17.55   13.471%   $19.9142   $19.91   $19.90   $19.90  
  Purchase #3 $227.49   12.513%   $255.9558   $255.96   $255.95   $256.00  
  Purchase #4 $233.50   8.222%   $252.6984   $252.70   $252.70   $252.70  
  Purchase #5 $120.37   5.698%   $127.2287   $127.23   $127.25   $127.20  
  Purchase #6 $15.49   7.583%   $16.6646   $16.66   $16.65   $16.70  
  Purchase #7 $93.42   6.534%   $99.5241   $99.52   $99.50   $99.50  
  7 purchase totals = $826.43       $896.2938   $896.29   $896.25   $896.30