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	$52.73	4.832%	$55.2779	$55.28	$55.30	$55.30
Purchase #2	$111.51	13.253%	$126.2884	$126.29	$126.30	$126.30
Purchase #3	$29.80	6.846%	$31.8401	$31.84	$31.85	$31.80
Purchase #4	$36.87	6.666%	$39.3278	$39.33	$39.35	$39.30
Purchase #5	$95.76	6.766%	$102.2391	$102.24	$102.25	$102.20
Purchase #6	$94.42	4.290%	$98.4706	$98.47	$98.45	$98.50
Purchase #7	$59.53	7.627%	$64.0704	$64.07	$64.05	$64.10
7 purchase totals =	$480.62		$517.5143	$517.52	$517.55	$517.50