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	$61.91	4.220%	$64.5226	$64.52	$64.50	$64.50
Purchase #2	$167.75	13.518%	$190.4264	$190.43	$190.45	$190.40
Purchase #3	$37.82	6.390%	$40.2367	$40.24	$40.25	$40.20
Purchase #4	$160.89	12.227%	$180.562	$180.56	$180.55	$180.60
Purchase #5	$86.84	3.575%	$89.9445	$89.94	$89.95	$89.90
Purchase #6	$56.89	5.736%	$60.1532	$60.15	$60.15	$60.20
Purchase #7	$19.74	5.566%	$20.8387	$20.84	$20.85	$20.80
7 purchase totals =	$591.84		$646.6841	$646.68	$646.70	$646.60