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	$34.91	6.123%	$37.0475	$37.05	$37.05	$37.00
Purchase #2	$79.93	13.383%	$90.627	$90.63	$90.65	$90.60
Purchase #3	$190.80	10.301%	$210.4543	$210.45	$210.45	$210.50
Purchase #4	$74.32	8.630%	$80.7338	$80.73	$80.75	$80.70
Purchase #5	$124.50	13.377%	$141.1544	$141.15	$141.15	$141.20
Purchase #6	$41.65	13.470%	$47.2603	$47.26	$47.25	$47.30
Purchase #7	$42.57	10.133%	$46.8836	$46.88	$46.90	$46.90
7 purchase totals =	$588.68		$654.1609	$654.15	$654.20	$654.20