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	$188.81	3.816%	$196.015	$196.02	$196.00	$196.00
Purchase #2	$89.84	12.760%	$101.3036	$101.30	$101.30	$101.30
Purchase #3	$211.88	5.646%	$223.8427	$223.84	$223.85	$223.80
Purchase #4	$51.88	6.762%	$55.3881	$55.39	$55.40	$55.40
Purchase #5	$139.28	10.591%	$154.0311	$154.03	$154.05	$154.00
Purchase #6	$80.69	5.858%	$85.4168	$85.42	$85.40	$85.40
Purchase #7	$202.85	10.103%	$223.3439	$223.34	$223.35	$223.30
7 purchase totals =	$965.23		$1,039.3412	$1,039.34	$1,039.35	$1,039.20