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 $236.99   10.573%   $262.047   $262.05   $262.05   $262.00  
  Purchase #2 $12.77   10.114%   $14.0616   $14.06   $14.05   $14.10  
  Purchase #3 $57.98   13.367%   $65.7302   $65.73   $65.75   $65.70  
  Purchase #4 $72.95   13.707%   $82.9493   $82.95   $82.95   $82.90  
  Purchase #5 $45.27   5.196%   $47.6222   $47.62   $47.60   $47.60  
  Purchase #6 $55.53   6.164%   $58.9529   $58.95   $58.95   $59.00  
  Purchase #7 $111.65   3.744%   $115.8302   $115.83   $115.85   $115.80  
  7 purchase totals = $593.14       $647.1934   $647.19   $647.20   $647.10