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 $62.45   10.844%   $69.2221   $69.22   $69.20   $69.20  
  Purchase #2 $180.90   12.674%   $203.8273   $203.83   $203.85   $203.80  
  Purchase #3 $172.48   5.312%   $181.6421   $181.64   $181.65   $181.60  
  Purchase #4 $85.38   7.402%   $91.6998   $91.70   $91.70   $91.70  
  Purchase #5 $70.59   4.764%   $73.9529   $73.95   $73.95   $74.00  
  Purchase #6 $102.75   12.198%   $115.2834   $115.28   $115.30   $115.30  
  Purchase #7 $208.57   6.426%   $221.9727   $221.97   $221.95   $222.00  
  7 purchase totals = $883.12       $957.6003   $957.59   $957.60   $957.60