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 $63.98   7.251%   $68.6192   $68.62   $68.60   $68.60  
  Purchase #2 $135.36   3.695%   $140.3616   $140.36   $140.35   $140.40  
  Purchase #3 $61.39   10.489%   $67.8292   $67.83   $67.85   $67.80  
  Purchase #4 $242.48   8.225%   $262.424   $262.42   $262.40   $262.40  
  Purchase #5 $224.62   13.450%   $254.8314   $254.83   $254.85   $254.80  
  Purchase #6 $239.83   3.164%   $247.4182   $247.42   $247.40   $247.40  
  Purchase #7 $235.88   11.105%   $262.0745   $262.07   $262.05   $262.10  
  7 purchase totals = $1,203.54       $1,303.5581   $1,303.55   $1,303.50   $1,303.50