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 $69.92   5.784%   $73.9642   $73.96   $73.95   $74.00  
  Purchase #2 $186.83   10.624%   $206.6788   $206.68   $206.70   $206.70  
  Purchase #3 $239.59   12.346%   $269.1698   $269.17   $269.15   $269.20  
  Purchase #4 $199.51   7.857%   $215.1855   $215.19   $215.20   $215.20  
  Purchase #5 $64.34   11.710%   $71.8742   $71.87   $71.85   $71.90  
  Purchase #6 $197.41   4.325%   $205.948   $205.95   $205.95   $205.90  
  Purchase #7 $219.97   9.243%   $240.3018   $240.30   $240.30   $240.30  
  7 purchase totals = $1,177.57       $1,283.1223   $1,283.12   $1,283.10   $1,283.20