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	$112.63	12.417%	$126.6153	$126.62	$126.60	$126.60
Purchase #2	$103.31	5.782%	$109.2834	$109.28	$109.30	$109.30
Purchase #3	$29.78	3.853%	$30.9274	$30.93	$30.95	$30.90
Purchase #4	$6.89	7.174%	$7.3843	$7.38	$7.40	$7.40
Purchase #5	$139.77	5.728%	$147.776	$147.78	$147.80	$147.80
Purchase #6	$175.59	3.277%	$181.3441	$181.34	$181.35	$181.30
Purchase #7	$200.93	9.223%	$219.4618	$219.46	$219.45	$219.50
7 purchase totals =	$768.90		$822.7923	$822.79	$822.85	$822.80