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	$231.27	5.128%	$243.1295	$243.13	$243.15	$243.10
Purchase #2	$83.98	7.842%	$90.5657	$90.57	$90.55	$90.60
Purchase #3	$146.89	4.439%	$153.4104	$153.41	$153.40	$153.40
Purchase #4	$46.82	7.402%	$50.2856	$50.29	$50.30	$50.30
Purchase #5	$146.45	8.566%	$158.9949	$158.99	$159.00	$159.00
Purchase #6	$145.54	4.455%	$152.0238	$152.02	$152.00	$152.00
Purchase #7	$236.34	12.272%	$265.3436	$265.34	$265.35	$265.30
7 purchase totals =	$1,037.29		$1,113.7535	$1,113.75	$1,113.75	$1,113.70