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 $227.81   5.601%   $240.5696   $240.57   $240.55   $240.60  
  Purchase #2 $116.38   4.799%   $121.9651   $121.97   $121.95   $122.00  
  Purchase #3 $203.44   5.383%   $214.3912   $214.39   $214.40   $214.40  
  Purchase #4 $95.27   6.290%   $101.2625   $101.26   $101.25   $101.30  
  Purchase #5 $83.83   13.787%   $95.3876   $95.39   $95.40   $95.40  
  Purchase #6 $178.27   9.232%   $194.7279   $194.73   $194.75   $194.70  
  Purchase #7 $142.28   7.682%   $153.2099   $153.21   $153.20   $153.20  
  7 purchase totals = $1,047.28       $1,121.5138   $1,121.52   $1,121.50   $1,121.60