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	$35.53	13.117%	$40.1905	$40.19	$40.20	$40.20
Purchase #2	$91.87	12.868%	$103.6918	$103.69	$103.70	$103.70
Purchase #3	$155.68	7.623%	$167.5475	$167.55	$167.55	$167.50
Purchase #4	$225.29	12.841%	$254.2195	$254.22	$254.20	$254.20
Purchase #5	$89.78	6.820%	$95.903	$95.90	$95.90	$95.90
Purchase #6	$127.37	9.760%	$139.8013	$139.80	$139.80	$139.80
Purchase #7	$132.46	10.565%	$146.4544	$146.45	$146.45	$146.50
7 purchase totals =	$857.98		$947.8080	$947.80	$947.80	$947.80