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	$35.28	3.714%	$36.5903	$36.59	$36.60	$36.60
Purchase #2	$74.77	9.455%	$81.8395	$81.84	$81.85	$81.80
Purchase #3	$222.65	7.512%	$239.3755	$239.38	$239.40	$239.40
Purchase #4	$117.69	8.315%	$127.4759	$127.48	$127.50	$127.50
Purchase #5	$80.52	11.479%	$89.7629	$89.76	$89.75	$89.80
Purchase #6	$55.53	8.641%	$60.3283	$60.33	$60.35	$60.30
Purchase #7	$64.63	9.262%	$70.616	$70.62	$70.60	$70.60
7 purchase totals =	$651.07		$705.9884	$706.00	$706.05	$706.00