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	$247.87	8.360%	$268.5919	$268.59	$268.60	$268.60
Purchase #2	$59.82	12.434%	$67.258	$67.26	$67.25	$67.30
Purchase #3	$17.55	3.518%	$18.1674	$18.17	$18.15	$18.20
Purchase #4	$74.99	13.679%	$85.2479	$85.25	$85.25	$85.20
Purchase #5	$26.58	4.647%	$27.8152	$27.82	$27.80	$27.80
Purchase #6	$188.59	11.236%	$209.78	$209.78	$209.80	$209.80
Purchase #7	$109.82	9.554%	$120.3122	$120.31	$120.30	$120.30
7 purchase totals =	$725.22		$797.1726	$797.18	$797.15	$797.20