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 $209.68   11.114%   $232.9838   $232.98   $233.00   $233.00  
  Purchase #2 $63.33   12.395%   $71.1798   $71.18   $71.20   $71.20  
  Purchase #3 $215.34   11.366%   $239.8155   $239.82   $239.80   $239.80  
  Purchase #4 $206.67   11.833%   $231.1253   $231.13   $231.15   $231.10  
  Purchase #5 $153.67   10.788%   $170.2479   $170.25   $170.25   $170.20  
  Purchase #6 $234.52   12.289%   $263.3402   $263.34   $263.35   $263.30  
  Purchase #7 $48.46   9.792%   $53.2052   $53.21   $53.20   $53.20  
  7 purchase totals = $1,131.67       $1,261.8977   $1,261.91   $1,261.95   $1,261.80