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 $250.73   12.545%   $282.1841   $282.18   $282.20   $282.20  
  Purchase #2 $191.64   6.839%   $204.7463   $204.75   $204.75   $204.70  
  Purchase #3 $99.66   8.732%   $108.3623   $108.36   $108.35   $108.40  
  Purchase #4 $168.78   10.849%   $187.0909   $187.09   $187.10   $187.10  
  Purchase #5 $152.57   11.782%   $170.5458   $170.55   $170.55   $170.50  
  Purchase #6 $147.66   4.333%   $154.0581   $154.06   $154.05   $154.10  
  Purchase #7 $126.90   9.771%   $139.2994   $139.30   $139.30   $139.30  
  7 purchase totals = $1,137.94       $1,246.2869   $1,246.29   $1,246.30   $1,246.30