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	$108.38	7.803%	$116.8369	$116.84	$116.85	$116.80
Purchase #2	$185.65	3.504%	$192.1552	$192.16	$192.15	$192.20
Purchase #3	$77.84	3.358%	$80.4539	$80.45	$80.45	$80.50
Purchase #4	$105.27	7.218%	$112.8684	$112.87	$112.85	$112.90
Purchase #5	$62.48	8.490%	$67.7846	$67.78	$67.80	$67.80
Purchase #6	$156.35	9.597%	$171.3549	$171.35	$171.35	$171.40
Purchase #7	$195.62	11.748%	$218.6014	$218.60	$218.60	$218.60
7 purchase totals =	$891.59		$960.0553	$960.05	$960.05	$960.20