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	$38.98	11.112%	$43.3115	$43.31	$43.30	$43.30
Purchase #2	$220.98	7.345%	$237.211	$237.21	$237.20	$237.20
Purchase #3	$229.86	12.398%	$258.358	$258.36	$258.35	$258.40
Purchase #4	$30.43	6.391%	$32.3748	$32.37	$32.35	$32.40
Purchase #5	$39.66	13.788%	$45.1283	$45.13	$45.15	$45.10
Purchase #6	$46.45	6.642%	$49.5352	$49.54	$49.55	$49.50
Purchase #7	$61.28	9.295%	$66.976	$66.98	$67.00	$67.00
7 purchase totals =	$667.64		$732.8948	$732.90	$732.90	$732.90