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 $23.28   8.602%   $25.2825   $25.28   $25.30   $25.30  
  Purchase #2 $250.63   10.218%   $276.2394   $276.24   $276.25   $276.20  
  Purchase #3 $58.30   3.741%   $60.481   $60.48   $60.50   $60.50  
  Purchase #4 $165.50   13.563%   $187.9468   $187.95   $187.95   $187.90  
  Purchase #5 $126.79   4.750%   $132.8125   $132.81   $132.80   $132.80  
  Purchase #6 $242.68   5.407%   $255.8017   $255.80   $255.80   $255.80  
  Purchase #7 $204.41   9.567%   $223.9659   $223.97   $223.95   $224.00  
  7 purchase totals = $1,071.59       $1,162.5298   $1,162.53   $1,162.55   $1,162.50