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	$15.65	5.284%	$16.4769	$16.48	$16.50	$16.50
Purchase #2	$173.76	11.262%	$193.3289	$193.33	$193.35	$193.30
Purchase #3	$77.48	10.650%	$85.7316	$85.73	$85.75	$85.70
Purchase #4	$42.29	10.107%	$46.5643	$46.56	$46.55	$46.60
Purchase #5	$92.98	11.335%	$103.5193	$103.52	$103.50	$103.50
Purchase #6	$175.48	5.591%	$185.2911	$185.29	$185.30	$185.30
Purchase #7	$125.58	13.657%	$142.7305	$142.73	$142.75	$142.70
7 purchase totals =	$703.22		$773.6426	$773.64	$773.70	$773.60