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 $88.84   6.300%   $94.4369   $94.44   $94.45   $94.40  
  Purchase #2 $205.59   3.337%   $212.4505   $212.45   $212.45   $212.50  
  Purchase #3 $104.43   9.746%   $114.6077   $114.61   $114.60   $114.60  
  Purchase #4 $142.59   9.320%   $155.8794   $155.88   $155.90   $155.90  
  Purchase #5 $117.31   5.156%   $123.3585   $123.36   $123.35   $123.40  
  Purchase #6 $224.35   5.428%   $236.5277   $236.53   $236.55   $236.50  
  Purchase #7 $18.69   5.264%   $19.6738   $19.67   $19.65   $19.70  
  7 purchase totals = $901.80       $956.9345   $956.94   $956.95   $957.00