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 $126.98   10.468%   $140.2723   $140.27   $140.25   $140.30  
  Purchase #2 $52.83   12.354%   $59.3566   $59.36   $59.35   $59.40  
  Purchase #3 $125.93   7.130%   $134.9088   $134.91   $134.90   $134.90  
  Purchase #4 $153.79   5.152%   $161.7133   $161.71   $161.70   $161.70  
  Purchase #5 $20.45   9.621%   $22.4175   $22.42   $22.40   $22.40  
  Purchase #6 $116.37   10.629%   $128.739   $128.74   $128.75   $128.70  
  Purchase #7 $113.28   10.839%   $125.5584   $125.56   $125.55   $125.60  
  7 purchase totals = $709.63       $772.9659   $772.97   $772.90   $773.00