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	$219.89	6.260%	$233.6551	$233.66	$233.65	$233.70
Purchase #2	$250.82	3.129%	$258.6682	$258.67	$258.65	$258.70
Purchase #3	$207.75	7.487%	$223.3042	$223.30	$223.30	$223.30
Purchase #4	$228.54	11.653%	$255.1718	$255.17	$255.15	$255.20
Purchase #5	$56.69	5.184%	$59.6288	$59.63	$59.65	$59.60
Purchase #6	$33.77	8.203%	$36.5402	$36.54	$36.55	$36.50
Purchase #7	$249.77	7.430%	$268.3279	$268.33	$268.35	$268.30
7 purchase totals =	$1,247.23		$1,335.2962	$1,335.30	$1,335.30	$1,335.30