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	$36.98	9.632%	$40.5419	$40.54	$40.55	$40.50
Purchase #2	$26.71	5.760%	$28.2485	$28.25	$28.25	$28.20
Purchase #3	$45.30	6.665%	$48.3192	$48.32	$48.30	$48.30
Purchase #4	$39.78	8.183%	$43.0352	$43.04	$43.05	$43.00
Purchase #5	$193.30	11.786%	$216.0823	$216.08	$216.10	$216.10
Purchase #6	$233.73	3.813%	$242.6421	$242.64	$242.65	$242.60
Purchase #7	$21.74	5.120%	$22.8531	$22.85	$22.85	$22.90
7 purchase totals =	$597.54		$641.7223	$641.72	$641.75	$641.60