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 $23.77   10.296%   $26.2174   $26.22   $26.20   $26.20  
  Purchase #2 $198.88   8.521%   $215.8266   $215.83   $215.85   $215.80  
  Purchase #3 $59.25   6.867%   $63.3187   $63.32   $63.30   $63.30  
  Purchase #4 $160.74   7.192%   $172.3004   $172.30   $172.30   $172.30  
  Purchase #5 $57.85   11.574%   $64.5456   $64.55   $64.55   $64.50  
  Purchase #6 $23.27   3.138%   $24.0002   $24.00   $24.00   $24.00  
  Purchase #7 $165.45   6.837%   $176.7618   $176.76   $176.75   $176.80  
  7 purchase totals = $689.21       $742.9707   $742.98   $742.95   $742.90