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 $94.81   3.394%   $98.0279   $98.03   $98.05   $98.00  
  Purchase #2 $139.58   10.554%   $154.3113   $154.31   $154.30   $154.30  
  Purchase #3 $59.27   3.264%   $61.2046   $61.20   $61.20   $61.20  
  Purchase #4 $123.25   5.446%   $129.9622   $129.96   $129.95   $130.00  
  Purchase #5 $72.62   5.158%   $76.3657   $76.37   $76.35   $76.40  
  Purchase #6 $246.35   11.528%   $274.7492   $274.75   $274.75   $274.70  
  Purchase #7 $116.37   6.399%   $123.8165   $123.82   $123.80   $123.80  
  7 purchase totals = $852.25       $918.4374   $918.44   $918.40   $918.40