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	$246.87	12.375%	$277.4202	$277.42	$277.40	$277.40
Purchase #2	$221.32	5.316%	$233.0854	$233.09	$233.10	$233.10
Purchase #3	$52.69	13.804%	$59.9633	$59.96	$59.95	$60.00
Purchase #4	$129.50	11.676%	$144.6204	$144.62	$144.60	$144.60
Purchase #5	$74.49	5.827%	$78.8305	$78.83	$78.85	$78.80
Purchase #6	$73.92	11.301%	$82.2737	$82.27	$82.25	$82.30
Purchase #7	$22.61	7.735%	$24.3589	$24.36	$24.35	$24.40
7 purchase totals =	$821.40		$900.5524	$900.55	$900.50	$900.60