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	$6.77	8.188%	$7.3243	$7.32	$7.30	$7.30
Purchase #2	$238.48	11.183%	$265.1492	$265.15	$265.15	$265.10
Purchase #3	$250.50	8.482%	$271.7474	$271.75	$271.75	$271.70
Purchase #4	$214.68	13.132%	$242.8718	$242.87	$242.85	$242.90
Purchase #5	$78.30	4.698%	$81.9785	$81.98	$82.00	$82.00
Purchase #6	$61.59	5.643%	$65.0655	$65.07	$65.05	$65.10
Purchase #7	$179.86	4.538%	$188.022	$188.02	$188.00	$188.00
7 purchase totals =	$1,030.18		$1,122.1587	$1,122.16	$1,122.10	$1,122.10