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	$82.50	12.866%	$93.1145	$93.11	$93.10	$93.10
Purchase #2	$158.29	5.743%	$167.3806	$167.38	$167.40	$167.40
Purchase #3	$49.59	13.259%	$56.1651	$56.17	$56.15	$56.20
Purchase #4	$74.97	11.674%	$83.722	$83.72	$83.70	$83.70
Purchase #5	$149.84	4.109%	$155.9969	$156.00	$156.00	$156.00
Purchase #6	$141.69	10.321%	$156.3138	$156.31	$156.30	$156.30
Purchase #7	$95.78	8.456%	$103.8792	$103.88	$103.90	$103.90
7 purchase totals =	$752.66		$816.5721	$816.57	$816.55	$816.60