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	$242.33	11.756%	$270.8183	$270.82	$270.80	$270.80
Purchase #2	$118.27	9.266%	$129.2289	$129.23	$129.25	$129.20
Purchase #3	$249.67	10.660%	$276.2848	$276.28	$276.30	$276.30
Purchase #4	$122.78	4.148%	$127.8729	$127.87	$127.85	$127.90
Purchase #5	$132.33	10.152%	$145.7641	$145.76	$145.75	$145.80
Purchase #6	$96.77	11.442%	$107.8424	$107.84	$107.85	$107.80
Purchase #7	$38.58	11.431%	$42.9901	$42.99	$43.00	$43.00
7 purchase totals =	$1,000.73		$1,100.8015	$1,100.79	$1,100.80	$1,100.80