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 $249.96   6.823%   $267.0148   $267.01   $267.00   $267.00  
  Purchase #2 $214.37   10.109%   $236.0407   $236.04   $236.05   $236.00  
  Purchase #3 $118.88   4.132%   $123.7921   $123.79   $123.80   $123.80  
  Purchase #4 $208.68   12.121%   $233.9741   $233.97   $233.95   $234.00  
  Purchase #5 $184.67   13.341%   $209.3068   $209.31   $209.30   $209.30  
  Purchase #6 $92.88   11.363%   $103.434   $103.43   $103.45   $103.40  
  Purchase #7 $222.93   13.604%   $253.2574   $253.26   $253.25   $253.30  
  7 purchase totals = $1,292.37       $1,426.8199   $1,426.81   $1,426.80   $1,426.80