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	$235.42	12.666%	$265.2383	$265.24	$265.25	$265.20
Purchase #2	$15.93	4.370%	$16.6261	$16.63	$16.65	$16.60
Purchase #3	$152.72	9.511%	$167.2452	$167.25	$167.25	$167.20
Purchase #4	$93.61	7.702%	$100.8198	$100.82	$100.80	$100.80
Purchase #5	$109.79	9.476%	$120.1937	$120.19	$120.20	$120.20
Purchase #6	$35.38	5.327%	$37.2647	$37.26	$37.25	$37.30
Purchase #7	$94.67	4.642%	$99.0646	$99.06	$99.05	$99.10
7 purchase totals =	$737.52		$806.4524	$806.45	$806.45	$806.40