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 $82.84   13.826%   $94.2935   $94.29   $94.30   $94.30  
  Purchase #2 $208.27   7.614%   $224.1277   $224.13   $224.15   $224.10  
  Purchase #3 $86.77   13.544%   $98.5221   $98.52   $98.50   $98.50  
  Purchase #4 $182.77   7.626%   $196.708   $196.71   $196.70   $196.70  
  Purchase #5 $222.91   7.723%   $240.1253   $240.13   $240.15   $240.10  
  Purchase #6 $202.80   11.377%   $225.8726   $225.87   $225.85   $225.90  
  Purchase #7 $219.76   12.134%   $246.4257   $246.43   $246.45   $246.40  
  7 purchase totals = $1,206.12       $1,326.0749   $1,326.08   $1,326.10   $1,326.00