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	$63.72	5.329%	$67.1156	$67.12	$67.10	$67.10
Purchase #2	$94.56	5.616%	$99.8705	$99.87	$99.85	$99.90
Purchase #3	$30.58	5.356%	$32.2179	$32.22	$32.20	$32.20
Purchase #4	$73.26	6.617%	$78.1076	$78.11	$78.10	$78.10
Purchase #5	$47.67	6.616%	$50.8238	$50.82	$50.80	$50.80
Purchase #6	$124.25	3.862%	$129.0485	$129.05	$129.05	$129.00
Purchase #7	$93.76	13.585%	$106.4973	$106.50	$106.50	$106.50
7 purchase totals =	$527.80		$563.6812	$563.69	$563.60	$563.60