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	$222.83	5.295%	$234.6288	$234.63	$234.65	$234.60
Purchase #2	$213.68	8.269%	$231.3492	$231.35	$231.35	$231.30
Purchase #3	$84.36	12.748%	$95.1142	$95.11	$95.10	$95.10
Purchase #4	$40.37	11.569%	$45.0404	$45.04	$45.05	$45.00
Purchase #5	$64.50	10.205%	$71.0822	$71.08	$71.10	$71.10
Purchase #6	$11.92	10.250%	$13.1418	$13.14	$13.15	$13.10
Purchase #7	$89.28	11.531%	$99.5749	$99.57	$99.55	$99.60
7 purchase totals =	$726.94		$789.9315	$789.92	$789.95	$789.80