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 $238.46   3.283%   $246.2886   $246.29   $246.30   $246.30  
  Purchase #2 $154.55   9.421%   $169.1102   $169.11   $169.10   $169.10  
  Purchase #3 $88.84   7.501%   $95.5039   $95.50   $95.50   $95.50  
  Purchase #4 $20.55   7.255%   $22.0409   $22.04   $22.05   $22.00  
  Purchase #5 $168.76   8.290%   $182.7502   $182.75   $182.75   $182.80  
  Purchase #6 $71.89   9.370%   $78.6261   $78.63   $78.65   $78.60  
  Purchase #7 $70.66   9.530%   $77.3939   $77.39   $77.40   $77.40  
  7 purchase totals = $813.71       $871.7138   $871.71   $871.75   $871.70