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 $115.68   7.235%   $124.0494   $124.05   $124.05   $124.00  
  Purchase #2 $191.92   13.278%   $217.4031   $217.40   $217.40   $217.40  
  Purchase #3 $23.68   11.672%   $26.4439   $26.44   $26.45   $26.40  
  Purchase #4 $102.90   12.862%   $116.135   $116.14   $116.15   $116.10  
  Purchase #5 $228.31   10.583%   $252.472   $252.47   $252.45   $252.50  
  Purchase #6 $75.67   11.614%   $84.4583   $84.46   $84.45   $84.50  
  Purchase #7 $198.98   11.796%   $222.4517   $222.45   $222.45   $222.50  
  7 purchase totals = $937.14       $1,043.4134   $1,043.41   $1,043.40   $1,043.40