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	$85.73	5.134%	$90.1314	$90.13	$90.15	$90.10
Purchase #2	$57.83	4.353%	$60.3473	$60.35	$60.35	$60.30
Purchase #3	$118.29	13.468%	$134.2213	$134.22	$134.20	$134.20
Purchase #4	$232.80	5.435%	$245.4527	$245.45	$245.45	$245.50
Purchase #5	$179.68	6.215%	$190.8471	$190.85	$190.85	$190.80
Purchase #6	$82.69	6.803%	$88.3154	$88.32	$88.30	$88.30
Purchase #7	$57.82	5.815%	$61.1822	$61.18	$61.20	$61.20
7 purchase totals =	$814.84		$870.4974	$870.50	$870.50	$870.40