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	$197.88	10.363%	$218.3863	$218.39	$218.40	$218.40
Purchase #2	$145.47	13.456%	$165.0444	$165.04	$165.05	$165.00
Purchase #3	$101.95	9.401%	$111.5343	$111.53	$111.55	$111.50
Purchase #4	$36.35	5.763%	$38.4449	$38.44	$38.45	$38.40
Purchase #5	$160.42	6.502%	$170.8505	$170.85	$170.85	$170.90
Purchase #6	$52.61	6.755%	$56.1638	$56.16	$56.15	$56.20
Purchase #7	$73.82	9.227%	$80.6314	$80.63	$80.65	$80.60
7 purchase totals =	$768.50		$841.0556	$841.04	$841.10	$841.00