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 $183.61   8.477%   $199.1746   $199.17   $199.15   $199.20  
  Purchase #2 $169.98   10.149%   $187.2313   $187.23   $187.25   $187.20  
  Purchase #3 $244.86   9.488%   $268.0923   $268.09   $268.10   $268.10  
  Purchase #4 $222.99   6.129%   $236.6571   $236.66   $236.65   $236.70  
  Purchase #5 $168.88   7.608%   $181.7284   $181.73   $181.75   $181.70  
  Purchase #6 $124.69   13.111%   $141.0381   $141.04   $141.05   $141.00  
  Purchase #7 $103.46   12.675%   $116.5736   $116.57   $116.55   $116.60  
  7 purchase totals = $1,218.47       $1,330.4954   $1,330.49   $1,330.50   $1,330.50