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	$14.28	13.149%	$16.1577	$16.16	$16.15	$16.20
Purchase #2	$99.55	13.637%	$113.1256	$113.13	$113.15	$113.10
Purchase #3	$78.42	5.404%	$82.6578	$82.66	$82.65	$82.70
Purchase #4	$26.74	11.197%	$29.7341	$29.73	$29.75	$29.70
Purchase #5	$62.93	3.789%	$65.3144	$65.31	$65.30	$65.30
Purchase #6	$152.76	6.272%	$162.3411	$162.34	$162.35	$162.30
Purchase #7	$72.89	12.686%	$82.1368	$82.14	$82.15	$82.10
7 purchase totals =	$507.57		$551.4675	$551.47	$551.50	$551.40