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 $204.78   9.549%   $224.3344   $224.33   $224.35   $224.30  
  Purchase #2 $162.47   7.640%   $174.8827   $174.88   $174.90   $174.90  
  Purchase #3 $86.53   13.574%   $98.2756   $98.28   $98.30   $98.30  
  Purchase #4 $235.46   4.230%   $245.42   $245.42   $245.40   $245.40  
  Purchase #5 $239.31   12.152%   $268.391   $268.39   $268.40   $268.40  
  Purchase #6 $242.56   7.242%   $260.1262   $260.13   $260.15   $260.10  
  Purchase #7 $17.82   8.502%   $19.3351   $19.34   $19.35   $19.30  
  7 purchase totals = $1,188.93       $1,290.7650   $1,290.77   $1,290.85   $1,290.70