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	$89.40	11.167%	$99.3833	$99.38	$99.40	$99.40
Purchase #2	$77.58	10.335%	$85.5979	$85.60	$85.60	$85.60
Purchase #3	$6.30	5.421%	$6.6415	$6.64	$6.65	$6.60
Purchase #4	$44.76	6.266%	$47.5647	$47.56	$47.55	$47.60
Purchase #5	$51.42	3.623%	$53.2829	$53.28	$53.30	$53.30
Purchase #6	$59.63	9.129%	$65.0736	$65.07	$65.05	$65.10
Purchase #7	$163.33	10.413%	$180.3376	$180.34	$180.35	$180.30
7 purchase totals =	$492.42		$537.8815	$537.87	$537.90	$537.90