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 $164.61   7.531%   $177.0068   $177.01   $177.00   $177.00  
  Purchase #2 $92.46   4.220%   $96.3618   $96.36   $96.35   $96.40  
  Purchase #3 $50.30   6.179%   $53.408   $53.41   $53.40   $53.40  
  Purchase #4 $234.85   8.874%   $255.6906   $255.69   $255.70   $255.70  
  Purchase #5 $116.98   4.443%   $122.1774   $122.18   $122.20   $122.20  
  Purchase #6 $66.53   11.827%   $74.3985   $74.40   $74.40   $74.40  
  Purchase #7 $21.81   7.715%   $23.4926   $23.49   $23.50   $23.50  
  7 purchase totals = $747.54       $802.5357   $802.54   $802.55   $802.60