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 $106.27   12.773%   $119.8439   $119.84   $119.85   $119.80  
  Purchase #2 $192.61   7.111%   $206.3065   $206.31   $206.30   $206.30  
  Purchase #3 $62.44   5.345%   $65.7774   $65.78   $65.80   $65.80  
  Purchase #4 $153.85   11.726%   $171.8905   $171.89   $171.90   $171.90  
  Purchase #5 $45.94   8.805%   $49.985   $49.99   $50.00   $50.00  
  Purchase #6 $196.56   12.796%   $221.7118   $221.71   $221.70   $221.70  
  Purchase #7 $168.25   12.457%   $189.2089   $189.21   $189.20   $189.20  
  7 purchase totals = $925.92       $1,024.7240   $1,024.73   $1,024.75   $1,024.70