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	$179.74	5.226%	$189.1332	$189.13	$189.15	$189.10
Purchase #2	$42.75	6.254%	$45.4236	$45.42	$45.40	$45.40
Purchase #3	$62.55	3.844%	$64.9544	$64.95	$64.95	$65.00
Purchase #4	$238.72	3.488%	$247.0466	$247.05	$247.05	$247.00
Purchase #5	$243.48	9.801%	$267.3435	$267.34	$267.35	$267.30
Purchase #6	$37.76	13.429%	$42.8308	$42.83	$42.85	$42.80
Purchase #7	$96.98	6.360%	$103.1479	$103.15	$103.15	$103.10
7 purchase totals =	$901.98		$959.8800	$959.87	$959.90	$959.70