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	$248.51	9.633%	$272.449	$272.45	$272.45	$272.40
Purchase #2	$111.60	12.142%	$125.1505	$125.15	$125.15	$125.20
Purchase #3	$40.38	11.586%	$45.0584	$45.06	$45.05	$45.10
Purchase #4	$237.50	3.539%	$245.9051	$245.91	$245.90	$245.90
Purchase #5	$109.62	13.535%	$124.4571	$124.46	$124.45	$124.50
Purchase #6	$237.48	7.701%	$255.7683	$255.77	$255.75	$255.80
Purchase #7	$203.74	7.431%	$218.8799	$218.88	$218.90	$218.90
7 purchase totals =	$1,188.83		$1,287.6683	$1,287.68	$1,287.65	$1,287.80