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	$98.98	10.731%	$109.6015	$109.60	$109.60	$109.60
Purchase #2	$158.82	13.596%	$180.4132	$180.41	$180.40	$180.40
Purchase #3	$24.55	8.261%	$26.5781	$26.58	$26.60	$26.60
Purchase #4	$185.79	3.141%	$191.6257	$191.63	$191.65	$191.60
Purchase #5	$14.62	4.134%	$15.2244	$15.22	$15.20	$15.20
Purchase #6	$72.41	13.844%	$82.4344	$82.43	$82.45	$82.40
Purchase #7	$123.28	3.351%	$127.4111	$127.41	$127.40	$127.40
7 purchase totals =	$678.45		$733.2884	$733.28	$733.30	$733.20