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	$16.25	3.527%	$16.8231	$16.82	$16.80	$16.80
Purchase #2	$181.57	7.558%	$195.2931	$195.29	$195.30	$195.30
Purchase #3	$97.34	8.354%	$105.4718	$105.47	$105.45	$105.50
Purchase #4	$63.89	12.427%	$71.8296	$71.83	$71.85	$71.80
Purchase #5	$128.42	4.438%	$134.1193	$134.12	$134.10	$134.10
Purchase #6	$196.28	4.501%	$205.1146	$205.11	$205.10	$205.10
Purchase #7	$77.72	10.176%	$85.6288	$85.63	$85.65	$85.60
7 purchase totals =	$761.47		$814.2803	$814.27	$814.25	$814.20