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 $60.89   9.403%   $66.6155   $66.62   $66.60   $66.60  
  Purchase #2 $107.62   7.453%   $115.6409   $115.64   $115.65   $115.60  
  Purchase #3 $166.75   12.850%   $188.1774   $188.18   $188.20   $188.20  
  Purchase #4 $220.76   9.708%   $242.1914   $242.19   $242.20   $242.20  
  Purchase #5 $104.84   9.608%   $114.913   $114.91   $114.90   $114.90  
  Purchase #6 $191.35   10.401%   $211.2523   $211.25   $211.25   $211.30  
  Purchase #7 $108.66   6.278%   $115.4817   $115.48   $115.50   $115.50  
  7 purchase totals = $960.87       $1,054.2722   $1,054.27   $1,054.30   $1,054.30