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	$175.96	3.155%	$181.5115	$181.51	$181.50	$181.50
Purchase #2	$127.53	9.603%	$139.7767	$139.78	$139.80	$139.80
Purchase #3	$147.30	8.236%	$159.4316	$159.43	$159.45	$159.40
Purchase #4	$129.72	13.594%	$147.3541	$147.35	$147.35	$147.40
Purchase #5	$35.74	8.785%	$38.8798	$38.88	$38.90	$38.90
Purchase #6	$96.66	9.462%	$105.806	$105.81	$105.80	$105.80
Purchase #7	$112.30	5.787%	$118.7988	$118.80	$118.80	$118.80
7 purchase totals =	$825.21		$891.5585	$891.56	$891.60	$891.60