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	$157.76	5.211%	$165.9809	$165.98	$166.00	$166.00
Purchase #2	$96.63	10.874%	$107.1375	$107.14	$107.15	$107.10
Purchase #3	$56.53	13.842%	$64.3549	$64.35	$64.35	$64.40
Purchase #4	$90.74	13.804%	$103.2657	$103.27	$103.25	$103.30
Purchase #5	$53.30	3.300%	$55.0589	$55.06	$55.05	$55.10
Purchase #6	$96.86	12.434%	$108.9036	$108.90	$108.90	$108.90
Purchase #7	$165.85	11.147%	$184.3373	$184.34	$184.35	$184.30
7 purchase totals =	$717.67		$789.0388	$789.04	$789.05	$789.10