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	$53.76	13.323%	$60.9224	$60.92	$60.90	$60.90
Purchase #2	$31.38	5.616%	$33.1423	$33.14	$33.15	$33.10
Purchase #3	$156.57	9.771%	$171.8685	$171.87	$171.85	$171.90
Purchase #4	$40.29	7.522%	$43.3206	$43.32	$43.30	$43.30
Purchase #5	$177.80	7.700%	$191.4906	$191.49	$191.50	$191.50
Purchase #6	$244.53	11.104%	$271.6826	$271.68	$271.70	$271.70
Purchase #7	$58.65	12.455%	$65.9549	$65.95	$65.95	$66.00
7 purchase totals =	$762.98		$838.3819	$838.37	$838.35	$838.40