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	$140.47	7.601%	$151.1471	$151.15	$151.15	$151.10
Purchase #2	$159.56	10.342%	$176.0617	$176.06	$176.05	$176.10
Purchase #3	$92.78	6.183%	$98.5166	$98.52	$98.50	$98.50
Purchase #4	$116.87	9.363%	$127.8125	$127.81	$127.80	$127.80
Purchase #5	$89.65	7.743%	$96.5916	$96.59	$96.60	$96.60
Purchase #6	$5.79	12.839%	$6.5334	$6.53	$6.55	$6.50
Purchase #7	$149.74	11.830%	$167.4542	$167.45	$167.45	$167.50
7 purchase totals =	$754.86		$824.1171	$824.11	$824.10	$824.10