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	$169.92	12.313%	$190.8422	$190.84	$190.85	$190.80
Purchase #2	$123.96	13.864%	$141.1458	$141.15	$141.15	$141.10
Purchase #3	$87.38	3.255%	$90.2242	$90.22	$90.20	$90.20
Purchase #4	$188.48	13.350%	$213.6421	$213.64	$213.65	$213.60
Purchase #5	$81.94	12.198%	$91.935	$91.94	$91.95	$91.90
Purchase #6	$104.89	3.324%	$108.3765	$108.38	$108.40	$108.40
Purchase #7	$75.91	13.636%	$86.2611	$86.26	$86.25	$86.30
7 purchase totals =	$832.48		$922.4269	$922.43	$922.45	$922.30