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	$39.70	7.603%	$42.7184	$42.72	$42.70	$42.70
Purchase #2	$19.40	9.501%	$21.2432	$21.24	$21.25	$21.20
Purchase #3	$34.63	7.465%	$37.2151	$37.22	$37.20	$37.20
Purchase #4	$209.69	6.695%	$223.7287	$223.73	$223.75	$223.70
Purchase #5	$76.30	4.211%	$79.513	$79.51	$79.50	$79.50
Purchase #6	$93.65	4.336%	$97.7107	$97.71	$97.70	$97.70
Purchase #7	$50.97	6.760%	$54.4156	$54.42	$54.40	$54.40
7 purchase totals =	$524.34		$556.5447	$556.55	$556.50	$556.40