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 $208.50   13.104%   $235.8218   $235.82   $235.80   $235.80  
  Purchase #2 $60.47   8.417%   $65.5598   $65.56   $65.55   $65.60  
  Purchase #3 $237.72   8.368%   $257.6124   $257.61   $257.60   $257.60  
  Purchase #4 $73.57   10.836%   $81.542   $81.54   $81.55   $81.50  
  Purchase #5 $132.34   4.150%   $137.8321   $137.83   $137.85   $137.80  
  Purchase #6 $46.39   3.539%   $48.0317   $48.03   $48.05   $48.00  
  Purchase #7 $200.43   8.138%   $216.741   $216.74   $216.75   $216.70  
  7 purchase totals = $959.42       $1,043.1408   $1,043.13   $1,043.15   $1,043.00