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 $209.51   8.513%   $227.3456   $227.35   $227.35   $227.30  
  Purchase #2 $110.50   4.377%   $115.3366   $115.34   $115.35   $115.30  
  Purchase #3 $234.69   4.258%   $244.6831   $244.68   $244.70   $244.70  
  Purchase #4 $169.93   10.125%   $187.1354   $187.14   $187.15   $187.10  
  Purchase #5 $176.26   5.788%   $186.4619   $186.46   $186.45   $186.50  
  Purchase #6 $65.64   11.131%   $72.9464   $72.95   $72.95   $72.90  
  Purchase #7 $27.41   13.262%   $31.0451   $31.05   $31.05   $31.00  
  7 purchase totals = $993.94       $1,064.9541   $1,064.97   $1,065.00   $1,064.80