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 $224.72   12.672%   $253.1965   $253.20   $253.20   $253.20  
  Purchase #2 $89.74   5.418%   $94.6021   $94.60   $94.60   $94.60  
  Purchase #3 $83.64   3.812%   $86.8284   $86.83   $86.85   $86.80  
  Purchase #4 $206.87   5.574%   $218.4009   $218.40   $218.40   $218.40  
  Purchase #5 $54.84   9.609%   $60.1096   $60.11   $60.10   $60.10  
  Purchase #6 $202.94   3.499%   $210.0409   $210.04   $210.05   $210.00  
  Purchase #7 $211.82   10.678%   $234.4381   $234.44   $234.45   $234.40  
  7 purchase totals = $1,074.57       $1,157.6165   $1,157.62   $1,157.65   $1,157.50