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 $212.91   10.181%   $234.5864   $234.59   $234.60   $234.60  
  Purchase #2 $125.94   9.117%   $137.4219   $137.42   $137.40   $137.40  
  Purchase #3 $64.61   3.338%   $66.7667   $66.77   $66.75   $66.80  
  Purchase #4 $98.83   4.441%   $103.219   $103.22   $103.20   $103.20  
  Purchase #5 $160.89   11.303%   $179.0754   $179.08   $179.10   $179.10  
  Purchase #6 $241.48   7.392%   $259.3302   $259.33   $259.35   $259.30  
  Purchase #7 $239.71   11.304%   $266.8068   $266.81   $266.80   $266.80  
  7 purchase totals = $1,144.37       $1,247.2064   $1,247.22   $1,247.20   $1,247.20