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	$173.96	11.131%	$193.3235	$193.32	$193.30	$193.30
Purchase #2	$179.51	10.808%	$198.9114	$198.91	$198.90	$198.90
Purchase #3	$29.31	12.451%	$32.9594	$32.96	$32.95	$33.00
Purchase #4	$168.37	12.824%	$189.9618	$189.96	$189.95	$190.00
Purchase #5	$38.38	6.192%	$40.7565	$40.76	$40.75	$40.80
Purchase #6	$65.72	10.215%	$72.4333	$72.43	$72.45	$72.40
Purchase #7	$19.57	12.725%	$22.0603	$22.06	$22.05	$22.10
7 purchase totals =	$674.82		$750.4062	$750.40	$750.35	$750.50