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 $56.43   13.165%   $63.859   $63.86   $63.85   $63.90  
  Purchase #2 $161.69   4.545%   $169.0388   $169.04   $169.05   $169.00  
  Purchase #3 $244.28   4.259%   $254.6839   $254.68   $254.70   $254.70  
  Purchase #4 $89.85   13.480%   $101.9618   $101.96   $101.95   $102.00  
  Purchase #5 $8.58   6.421%   $9.1309   $9.13   $9.15   $9.10  
  Purchase #6 $106.36   5.590%   $112.3055   $112.31   $112.30   $112.30  
  Purchase #7 $15.57   8.559%   $16.9026   $16.90   $16.90   $16.90  
  7 purchase totals = $682.76       $727.8825   $727.88   $727.90   $727.90