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 $99.81   9.680%   $109.4716   $109.47   $109.45   $109.50  
  Purchase #2 $146.64   3.171%   $151.29   $151.29   $151.30   $151.30  
  Purchase #3 $102.94   13.285%   $116.6156   $116.62   $116.60   $116.60  
  Purchase #4 $75.70   9.393%   $82.8105   $82.81   $82.80   $82.80  
  Purchase #5 $102.98   12.385%   $115.7341   $115.73   $115.75   $115.70  
  Purchase #6 $53.40   4.208%   $55.6471   $55.65   $55.65   $55.60  
  Purchase #7 $213.87   8.839%   $232.774   $232.77   $232.75   $232.80  
  7 purchase totals = $795.34       $864.3429   $864.34   $864.30   $864.30