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 $208.95   8.696%   $227.1203   $227.12   $227.10   $227.10  
  Purchase #2 $244.51   12.233%   $274.4209   $274.42   $274.40   $274.40  
  Purchase #3 $132.62   4.684%   $138.8319   $138.83   $138.85   $138.80  
  Purchase #4 $123.85   10.236%   $136.5273   $136.53   $136.55   $136.50  
  Purchase #5 $232.74   5.449%   $245.422   $245.42   $245.40   $245.40  
  Purchase #6 $90.44   11.850%   $101.1571   $101.16   $101.15   $101.20  
  Purchase #7 $49.73   6.216%   $52.8212   $52.82   $52.80   $52.80  
  7 purchase totals = $1,082.84       $1,176.3007   $1,176.30   $1,176.25   $1,176.20