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 $82.86   13.864%   $94.3477   $94.35   $94.35   $94.30  
  Purchase #2 $110.97   9.677%   $121.7086   $121.71   $121.70   $121.70  
  Purchase #3 $29.36   7.614%   $31.5955   $31.60   $31.60   $31.60  
  Purchase #4 $245.25   5.342%   $258.3513   $258.35   $258.35   $258.40  
  Purchase #5 $219.28   3.537%   $227.0359   $227.04   $227.05   $227.00  
  Purchase #6 $215.60   8.433%   $233.7815   $233.78   $233.80   $233.80  
  Purchase #7 $83.75   10.176%   $92.2724   $92.27   $92.25   $92.30  
  7 purchase totals = $987.07       $1,059.0929   $1,059.10   $1,059.10   $1,059.10