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 $225.61   12.475%   $253.7548   $253.75   $253.75   $253.80  
  Purchase #2 $154.92   12.603%   $174.4446   $174.44   $174.45   $174.40  
  Purchase #3 $223.33   4.457%   $233.2838   $233.28   $233.30   $233.30  
  Purchase #4 $179.97   6.505%   $191.677   $191.68   $191.70   $191.70  
  Purchase #5 $24.71   12.282%   $27.7449   $27.74   $27.75   $27.70  
  Purchase #6 $28.64   12.407%   $32.1934   $32.19   $32.20   $32.20  
  Purchase #7 $92.32   10.219%   $101.7542   $101.75   $101.75   $101.80  
  7 purchase totals = $929.50       $1,014.8527   $1,014.83   $1,014.90   $1,014.90