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	$90.43	11.110%	$100.4768	$100.48	$100.50	$100.50
Purchase #2	$140.59	10.444%	$155.2732	$155.27	$155.25	$155.30
Purchase #3	$162.33	8.153%	$175.5648	$175.56	$175.55	$175.60
Purchase #4	$114.51	8.778%	$124.5617	$124.56	$124.55	$124.60
Purchase #5	$152.73	4.539%	$159.6624	$159.66	$159.65	$159.70
Purchase #6	$27.63	5.485%	$29.1455	$29.15	$29.15	$29.10
Purchase #7	$157.34	8.730%	$171.0758	$171.08	$171.10	$171.10
7 purchase totals =	$845.56		$915.7602	$915.76	$915.75	$915.90