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	$52.42	9.244%	$57.2657	$57.27	$57.25	$57.30
Purchase #2	$177.63	11.481%	$198.0237	$198.02	$198.00	$198.00
Purchase #3	$160.74	6.411%	$171.045	$171.05	$171.05	$171.00
Purchase #4	$70.64	5.726%	$74.6848	$74.68	$74.70	$74.70
Purchase #5	$93.82	10.468%	$103.6411	$103.64	$103.65	$103.60
Purchase #6	$135.92	10.448%	$150.1209	$150.12	$150.10	$150.10
Purchase #7	$55.32	7.545%	$59.4939	$59.49	$59.50	$59.50
7 purchase totals =	$746.49		$814.2751	$814.27	$814.25	$814.20