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	$34.45	9.714%	$37.7965	$37.80	$37.80	$37.80
Purchase #2	$83.53	5.768%	$88.348	$88.35	$88.35	$88.30
Purchase #3	$73.35	5.338%	$77.2654	$77.27	$77.25	$77.30
Purchase #4	$154.57	8.247%	$167.3174	$167.32	$167.30	$167.30
Purchase #5	$47.72	12.391%	$53.633	$53.63	$53.65	$53.60
Purchase #6	$89.61	13.641%	$101.8337	$101.83	$101.85	$101.80
Purchase #7	$67.80	5.106%	$71.2619	$71.26	$71.25	$71.30
7 purchase totals =	$551.03		$597.4559	$597.46	$597.45	$597.40