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 $221.32   11.112%   $245.9131   $245.91   $245.90   $245.90  
  Purchase #2 $126.90   9.789%   $139.3222   $139.32   $139.30   $139.30  
  Purchase #3 $106.55   13.684%   $121.1303   $121.13   $121.15   $121.10  
  Purchase #4 $244.85   3.386%   $253.1406   $253.14   $253.15   $253.10  
  Purchase #5 $71.90   3.857%   $74.6732   $74.67   $74.65   $74.70  
  Purchase #6 $36.45   11.397%   $40.6042   $40.60   $40.60   $40.60  
  Purchase #7 $67.85   12.672%   $76.448   $76.45   $76.45   $76.40  
  7 purchase totals = $875.82       $951.2316   $951.22   $951.20   $951.10