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	$212.74	10.240%	$234.5246	$234.52	$234.50	$234.50
Purchase #2	$122.72	7.303%	$131.6822	$131.68	$131.70	$131.70
Purchase #3	$6.89	7.148%	$7.3825	$7.38	$7.40	$7.40
Purchase #4	$54.74	3.128%	$56.4523	$56.45	$56.45	$56.50
Purchase #5	$123.47	11.393%	$137.5369	$137.54	$137.55	$137.50
Purchase #6	$18.55	6.396%	$19.7365	$19.74	$19.75	$19.70
Purchase #7	$62.85	13.170%	$71.1273	$71.13	$71.15	$71.10
7 purchase totals =	$601.96		$658.4423	$658.44	$658.50	$658.40