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	$203.26	8.618%	$220.7769	$220.78	$220.80	$220.80
Purchase #2	$158.43	4.859%	$166.1281	$166.13	$166.15	$166.10
Purchase #3	$35.73	5.623%	$37.7391	$37.74	$37.75	$37.70
Purchase #4	$185.90	10.283%	$205.0161	$205.02	$205.00	$205.00
Purchase #5	$28.80	3.492%	$29.8057	$29.81	$29.80	$29.80
Purchase #6	$77.82	9.514%	$85.2238	$85.22	$85.20	$85.20
Purchase #7	$222.83	11.695%	$248.89	$248.89	$248.90	$248.90
7 purchase totals =	$912.77		$993.5797	$993.59	$993.60	$993.50