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	$185.58	6.405%	$197.4664	$197.47	$197.45	$197.50
Purchase #2	$115.59	12.111%	$129.5891	$129.59	$129.60	$129.60
Purchase #3	$227.38	7.722%	$244.9383	$244.94	$244.95	$244.90
Purchase #4	$171.72	11.327%	$191.1707	$191.17	$191.15	$191.20
Purchase #5	$88.94	11.487%	$99.1565	$99.16	$99.15	$99.20
Purchase #6	$37.62	10.598%	$41.607	$41.61	$41.60	$41.60
Purchase #7	$198.44	5.379%	$209.1141	$209.11	$209.10	$209.10
7 purchase totals =	$1,025.27		$1,113.0421	$1,113.05	$1,113.00	$1,113.10