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 $84.94   12.782%   $95.797   $95.80   $95.80   $95.80  
  Purchase #2 $249.60   8.522%   $270.8709   $270.87   $270.85   $270.90  
  Purchase #3 $224.76   12.148%   $252.0638   $252.06   $252.05   $252.10  
  Purchase #4 $89.96   4.333%   $93.858   $93.86   $93.85   $93.90  
  Purchase #5 $115.33   9.443%   $126.2206   $126.22   $126.20   $126.20  
  Purchase #6 $231.68   10.147%   $255.1886   $255.19   $255.20   $255.20  
  Purchase #7 $145.63   10.749%   $161.2838   $161.28   $161.30   $161.30  
  7 purchase totals = $1,141.90       $1,255.2827   $1,255.28   $1,255.25   $1,255.40