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 $216.50   11.344%   $241.0598   $241.06   $241.05   $241.10  
  Purchase #2 $142.37   9.261%   $155.5549   $155.55   $155.55   $155.60  
  Purchase #3 $239.97   11.313%   $267.1178   $267.12   $267.10   $267.10  
  Purchase #4 $249.54   5.130%   $262.3414   $262.34   $262.35   $262.30  
  Purchase #5 $213.86   9.451%   $234.0719   $234.07   $234.05   $234.10  
  Purchase #6 $210.79   11.699%   $235.4503   $235.45   $235.45   $235.50  
  Purchase #7 $152.73   4.318%   $159.3249   $159.32   $159.30   $159.30  
  7 purchase totals = $1,425.76       $1,554.9210   $1,554.91   $1,554.85   $1,555.00