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	$74.70	3.406%	$77.2443	$77.24	$77.25	$77.20
Purchase #2	$242.71	8.858%	$264.2093	$264.21	$264.20	$264.20
Purchase #3	$167.76	10.398%	$185.2037	$185.20	$185.20	$185.20
Purchase #4	$91.43	13.188%	$103.4878	$103.49	$103.50	$103.50
Purchase #5	$97.86	5.363%	$103.1082	$103.11	$103.10	$103.10
Purchase #6	$40.97	4.419%	$42.7805	$42.78	$42.80	$42.80
Purchase #7	$185.27	9.492%	$202.8558	$202.86	$202.85	$202.90
7 purchase totals =	$900.70		$978.8896	$978.89	$978.90	$978.90