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	$5.65	6.862%	$6.0377	$6.04	$6.05	$6.00
Purchase #2	$20.91	8.464%	$22.6798	$22.68	$22.70	$22.70
Purchase #3	$174.45	12.486%	$196.2318	$196.23	$196.25	$196.20
Purchase #4	$47.96	9.433%	$52.4841	$52.48	$52.50	$52.50
Purchase #5	$104.49	13.369%	$118.4593	$118.46	$118.45	$118.50
Purchase #6	$62.83	7.222%	$67.3676	$67.37	$67.35	$67.40
Purchase #7	$93.26	6.668%	$99.4786	$99.48	$99.50	$99.50
7 purchase totals =	$509.55		$562.7389	$562.74	$562.80	$562.80