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 $181.51   13.789%   $206.5384   $206.54   $206.55   $206.50  
  Purchase #2 $53.82   10.272%   $59.3484   $59.35   $59.35   $59.30  
  Purchase #3 $25.43   6.579%   $27.103   $27.10   $27.10   $27.10  
  Purchase #4 $204.53   5.318%   $215.4069   $215.41   $215.40   $215.40  
  Purchase #5 $138.74   11.624%   $154.8671   $154.87   $154.85   $154.90  
  Purchase #6 $125.42   10.694%   $138.8324   $138.83   $138.85   $138.80  
  Purchase #7 $227.79   8.664%   $247.5257   $247.53   $247.55   $247.50  
  7 purchase totals = $957.24       $1,049.6219   $1,049.63   $1,049.65   $1,049.50