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 $227.37   10.745%   $251.8009   $251.80   $251.80   $251.80  
  Purchase #2 $227.94   13.188%   $258.0007   $258.00   $258.00   $258.00  
  Purchase #3 $248.91   12.726%   $280.5863   $280.59   $280.60   $280.60  
  Purchase #4 $206.29   13.343%   $233.8153   $233.82   $233.80   $233.80  
  Purchase #5 $45.50   5.310%   $47.9161   $47.92   $47.90   $47.90  
  Purchase #6 $111.44   11.531%   $124.2901   $124.29   $124.30   $124.30  
  Purchase #7 $202.78   12.398%   $227.9207   $227.92   $227.90   $227.90  
  7 purchase totals = $1,270.23       $1,424.3301   $1,424.34   $1,424.30   $1,424.30