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 $60.58   4.226%   $63.1401   $63.14   $63.15   $63.10  
  Purchase #2 $28.33   4.456%   $29.5924   $29.59   $29.60   $29.60  
  Purchase #3 $235.89   10.684%   $261.0925   $261.09   $261.10   $261.10  
  Purchase #4 $216.25   3.255%   $223.2889   $223.29   $223.30   $223.30  
  Purchase #5 $127.89   3.227%   $132.017   $132.02   $132.00   $132.00  
  Purchase #6 $121.75   13.844%   $138.6051   $138.61   $138.60   $138.60  
  Purchase #7 $172.29   8.389%   $186.7434   $186.74   $186.75   $186.70  
  7 purchase totals = $962.98       $1,034.4794   $1,034.48   $1,034.50   $1,034.40