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	$155.71	8.242%	$168.5436	$168.54	$168.55	$168.50
Purchase #2	$138.48	10.242%	$152.6631	$152.66	$152.65	$152.70
Purchase #3	$114.70	4.114%	$119.4188	$119.42	$119.40	$119.40
Purchase #4	$79.57	5.219%	$83.7228	$83.72	$83.70	$83.70
Purchase #5	$10.70	12.595%	$12.0477	$12.05	$12.05	$12.00
Purchase #6	$85.96	4.868%	$90.1445	$90.14	$90.15	$90.10
Purchase #7	$250.97	6.801%	$268.0385	$268.04	$268.05	$268.00
7 purchase totals =	$836.09		$894.5790	$894.57	$894.55	$894.40