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	$249.53	8.543%	$270.8473	$270.85	$270.85	$270.80
Purchase #2	$195.37	6.250%	$207.5806	$207.58	$207.60	$207.60
Purchase #3	$128.65	13.278%	$145.7321	$145.73	$145.75	$145.70
Purchase #4	$85.36	5.306%	$89.8892	$89.89	$89.90	$89.90
Purchase #5	$118.26	10.345%	$130.494	$130.49	$130.50	$130.50
Purchase #6	$50.96	12.702%	$57.4329	$57.43	$57.45	$57.40
Purchase #7	$129.58	12.123%	$145.289	$145.29	$145.30	$145.30
7 purchase totals =	$957.71		$1,047.2651	$1,047.26	$1,047.35	$1,047.20