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 $63.54   8.518%   $68.9523   $68.95   $68.95   $69.00  
  Purchase #2 $53.47   4.558%   $55.9072   $55.91   $55.90   $55.90  
  Purchase #3 $166.97   4.162%   $173.9193   $173.92   $173.90   $173.90  
  Purchase #4 $214.94   8.322%   $232.8273   $232.83   $232.85   $232.80  
  Purchase #5 $182.89   5.872%   $193.6293   $193.63   $193.65   $193.60  
  Purchase #6 $76.86   3.319%   $79.411   $79.41   $79.40   $79.40  
  Purchase #7 $96.70   8.276%   $104.7029   $104.70   $104.70   $104.70  
  7 purchase totals = $855.37       $909.3493   $909.35   $909.35   $909.30