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	$170.86	6.741%	$182.3777	$182.38	$182.40	$182.40
Purchase #2	$173.49	10.644%	$191.9563	$191.96	$191.95	$192.00
Purchase #3	$229.32	9.184%	$250.3807	$250.38	$250.40	$250.40
Purchase #4	$222.63	6.654%	$237.4438	$237.44	$237.45	$237.40
Purchase #5	$136.82	10.405%	$151.0561	$151.06	$151.05	$151.10
Purchase #6	$157.30	7.118%	$168.4966	$168.50	$168.50	$168.50
Purchase #7	$45.47	5.284%	$47.8726	$47.87	$47.85	$47.90
7 purchase totals =	$1,135.89		$1,229.5838	$1,229.59	$1,229.60	$1,229.70