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	$25.83	8.251%	$27.9612	$27.96	$27.95	$28.00
Purchase #2	$218.83	4.426%	$228.5154	$228.52	$228.50	$228.50
Purchase #3	$128.27	8.538%	$139.2217	$139.22	$139.20	$139.20
Purchase #4	$47.59	5.835%	$50.3669	$50.37	$50.35	$50.40
Purchase #5	$16.85	11.845%	$18.8459	$18.85	$18.85	$18.80
Purchase #6	$117.44	9.552%	$128.6579	$128.66	$128.65	$128.70
Purchase #7	$93.50	13.724%	$106.3319	$106.33	$106.35	$106.30
7 purchase totals =	$648.31		$699.9009	$699.91	$699.85	$699.90