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 $57.62   13.256%   $65.2581   $65.26   $65.25   $65.30  
  Purchase #2 $246.77   12.207%   $276.8932   $276.89   $276.90   $276.90  
  Purchase #3 $195.34   9.292%   $213.491   $213.49   $213.50   $213.50  
  Purchase #4 $238.91   8.793%   $259.9174   $259.92   $259.90   $259.90  
  Purchase #5 $92.92   5.475%   $98.0074   $98.01   $98.00   $98.00  
  Purchase #6 $6.63   4.562%   $6.9325   $6.93   $6.95   $6.90  
  Purchase #7 $217.58   4.816%   $228.0587   $228.06   $228.05   $228.10  
  7 purchase totals = $1,055.77       $1,148.5583   $1,148.56   $1,148.55   $1,148.60