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	$249.62	10.403%	$275.588	$275.59	$275.60	$275.60
Purchase #2	$76.53	11.662%	$85.4549	$85.45	$85.45	$85.50
Purchase #3	$166.51	9.562%	$182.4317	$182.43	$182.45	$182.40
Purchase #4	$97.59	3.146%	$100.6602	$100.66	$100.65	$100.70
Purchase #5	$95.36	13.569%	$108.2994	$108.30	$108.30	$108.30
Purchase #6	$224.27	13.586%	$254.7393	$254.74	$254.75	$254.70
Purchase #7	$73.84	13.237%	$83.6142	$83.61	$83.60	$83.60
7 purchase totals =	$983.72		$1,090.7877	$1,090.78	$1,090.80	$1,090.80