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	$165.30	11.543%	$184.3806	$184.38	$184.40	$184.40
Purchase #2	$68.97	13.775%	$78.4706	$78.47	$78.45	$78.50
Purchase #3	$95.64	4.858%	$100.2862	$100.29	$100.30	$100.30
Purchase #4	$146.93	12.447%	$165.2184	$165.22	$165.20	$165.20
Purchase #5	$163.50	4.658%	$171.1158	$171.12	$171.10	$171.10
Purchase #6	$5.96	9.581%	$6.531	$6.53	$6.55	$6.50
Purchase #7	$78.35	9.530%	$85.8168	$85.82	$85.80	$85.80
7 purchase totals =	$724.65		$791.8194	$791.83	$791.80	$791.80