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 $236.83   5.508%   $249.8746   $249.87   $249.85   $249.90  
  Purchase #2 $209.77   6.221%   $222.8198   $222.82   $222.80   $222.80  
  Purchase #3 $158.80   11.153%   $176.511   $176.51   $176.50   $176.50  
  Purchase #4 $124.41   7.193%   $133.3588   $133.36   $133.35   $133.40  
  Purchase #5 $8.83   7.527%   $9.4946   $9.49   $9.50   $9.50  
  Purchase #6 $219.38   3.177%   $226.3497   $226.35   $226.35   $226.30  
  Purchase #7 $40.75   3.528%   $42.1877   $42.19   $42.20   $42.20  
  7 purchase totals = $998.77       $1,060.5962   $1,060.59   $1,060.55   $1,060.60