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	$51.83	4.568%	$54.1976	$54.20	$54.20	$54.20
Purchase #2	$242.54	13.316%	$274.8366	$274.84	$274.85	$274.80
Purchase #3	$71.60	10.563%	$79.1631	$79.16	$79.15	$79.20
Purchase #4	$42.96	7.300%	$46.0961	$46.10	$46.10	$46.10
Purchase #5	$226.79	10.592%	$250.8116	$250.81	$250.80	$250.80
Purchase #6	$102.30	3.126%	$105.4979	$105.50	$105.50	$105.50
Purchase #7	$183.73	6.846%	$196.3082	$196.31	$196.30	$196.30
7 purchase totals =	$921.75		$1,006.9111	$1,006.92	$1,006.90	$1,006.90