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	$250.30	7.730%	$269.6482	$269.65	$269.65	$269.60
Purchase #2	$35.26	13.446%	$40.0011	$40.00	$40.00	$40.00
Purchase #3	$140.33	6.505%	$149.4585	$149.46	$149.45	$149.50
Purchase #4	$154.88	4.161%	$161.3246	$161.32	$161.30	$161.30
Purchase #5	$139.94	4.723%	$146.5494	$146.55	$146.55	$146.50
Purchase #6	$238.48	5.190%	$250.8571	$250.86	$250.85	$250.90
Purchase #7	$154.32	8.420%	$167.3137	$167.31	$167.30	$167.30
7 purchase totals =	$1,113.51		$1,185.1526	$1,185.15	$1,185.10	$1,185.10