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	$223.47	6.789%	$238.6414	$238.64	$238.65	$238.60
Purchase #2	$16.33	11.654%	$18.2331	$18.23	$18.25	$18.20
Purchase #3	$157.65	13.592%	$179.0778	$179.08	$179.10	$179.10
Purchase #4	$53.78	5.452%	$56.7121	$56.71	$56.70	$56.70
Purchase #5	$130.51	13.347%	$147.9292	$147.93	$147.95	$147.90
Purchase #6	$26.30	6.871%	$28.1071	$28.11	$28.10	$28.10
Purchase #7	$209.60	6.178%	$222.5491	$222.55	$222.55	$222.50
7 purchase totals =	$817.64		$891.2498	$891.25	$891.30	$891.10