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 $63.50   10.197%   $69.9751   $69.98   $70.00   $70.00  
  Purchase #2 $176.94   8.703%   $192.3391   $192.34   $192.35   $192.30  
  Purchase #3 $85.80   11.191%   $95.4019   $95.40   $95.40   $95.40  
  Purchase #4 $244.70   13.594%   $277.9645   $277.96   $277.95   $278.00  
  Purchase #5 $156.62   4.655%   $163.9107   $163.91   $163.90   $163.90  
  Purchase #6 $204.63   13.845%   $232.961   $232.96   $232.95   $233.00  
  Purchase #7 $13.60   8.130%   $14.7057   $14.71   $14.70   $14.70  
  7 purchase totals = $945.79       $1,047.2580   $1,047.26   $1,047.25   $1,047.30