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	$17.33	5.123%	$18.2178	$18.22	$18.20	$18.20
Purchase #2	$84.94	10.822%	$94.1322	$94.13	$94.15	$94.10
Purchase #3	$53.30	11.670%	$59.5201	$59.52	$59.50	$59.50
Purchase #4	$68.63	11.389%	$76.4463	$76.45	$76.45	$76.40
Purchase #5	$24.98	6.154%	$26.5173	$26.52	$26.50	$26.50
Purchase #6	$29.76	3.793%	$30.8888	$30.89	$30.90	$30.90
Purchase #7	$102.58	6.411%	$109.1564	$109.16	$109.15	$109.20
7 purchase totals =	$381.52		$414.8789	$414.89	$414.85	$414.80