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	$57.82	6.244%	$61.4303	$61.43	$61.45	$61.40
Purchase #2	$159.45	3.700%	$165.3497	$165.35	$165.35	$165.30
Purchase #3	$79.70	12.462%	$89.6322	$89.63	$89.65	$89.60
Purchase #4	$43.77	10.392%	$48.3186	$48.32	$48.30	$48.30
Purchase #5	$227.98	11.690%	$254.6309	$254.63	$254.65	$254.60
Purchase #6	$125.69	13.735%	$142.9535	$142.95	$142.95	$143.00
Purchase #7	$155.83	9.348%	$170.397	$170.40	$170.40	$170.40
7 purchase totals =	$850.24		$932.7122	$932.71	$932.75	$932.60