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	$103.29	5.862%	$109.3449	$109.34	$109.35	$109.30
Purchase #2	$142.77	7.250%	$153.1208	$153.12	$153.10	$153.10
Purchase #3	$243.77	9.411%	$266.7112	$266.71	$266.70	$266.70
Purchase #4	$103.73	8.456%	$112.5014	$112.50	$112.50	$112.50
Purchase #5	$37.65	9.251%	$41.133	$41.13	$41.15	$41.10
Purchase #6	$67.42	8.764%	$73.3287	$73.33	$73.35	$73.30
Purchase #7	$162.58	13.345%	$184.2763	$184.28	$184.30	$184.30
7 purchase totals =	$861.21		$940.4163	$940.41	$940.45	$940.30