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 $186.78   8.377%   $202.4266   $202.43   $202.45   $202.40  
  Purchase #2 $224.61   5.344%   $236.6132   $236.61   $236.60   $236.60  
  Purchase #3 $74.42   7.110%   $79.7113   $79.71   $79.70   $79.70  
  Purchase #4 $126.72   4.383%   $132.2741   $132.27   $132.25   $132.30  
  Purchase #5 $207.94   12.338%   $233.5956   $233.60   $233.60   $233.60  
  Purchase #6 $168.27   4.475%   $175.8001   $175.80   $175.80   $175.80  
  Purchase #7 $167.81   9.577%   $183.8812   $183.88   $183.90   $183.90  
  7 purchase totals = $1,156.55       $1,244.3021   $1,244.30   $1,244.30   $1,244.30