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 $183.31   10.491%   $202.5411   $202.54   $202.55   $202.50  
  Purchase #2 $229.56   3.559%   $237.73   $237.73   $237.75   $237.70  
  Purchase #3 $76.36   5.463%   $80.5315   $80.53   $80.55   $80.50  
  Purchase #4 $74.86   11.106%   $83.174   $83.17   $83.15   $83.20  
  Purchase #5 $24.60   9.798%   $27.0103   $27.01   $27.00   $27.00  
  Purchase #6 $117.63   13.826%   $133.8935   $133.89   $133.90   $133.90  
  Purchase #7 $40.31   13.821%   $45.8812   $45.88   $45.90   $45.90  
  7 purchase totals = $746.63       $810.7616   $810.75   $810.80   $810.70