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 $66.60   4.478%   $69.5823   $69.58   $69.60   $69.60  
  Purchase #2 $198.89   5.553%   $209.9344   $209.93   $209.95   $209.90  
  Purchase #3 $168.95   9.519%   $185.0324   $185.03   $185.05   $185.00  
  Purchase #4 $166.84   5.743%   $176.4216   $176.42   $176.40   $176.40  
  Purchase #5 $192.27   5.583%   $203.0044   $203.00   $203.00   $203.00  
  Purchase #6 $159.72   5.458%   $168.4375   $168.44   $168.45   $168.40  
  Purchase #7 $193.36   9.644%   $212.0076   $212.01   $212.00   $212.00  
  7 purchase totals = $1,146.63       $1,224.4202   $1,224.41   $1,224.45   $1,224.30