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	$226.70	3.293%	$234.1652	$234.17	$234.15	$234.20
Purchase #2	$122.64	4.689%	$128.3906	$128.39	$128.40	$128.40
Purchase #3	$237.26	11.490%	$264.5212	$264.52	$264.50	$264.50
Purchase #4	$139.26	10.447%	$153.8085	$153.81	$153.80	$153.80
Purchase #5	$161.29	4.422%	$168.4222	$168.42	$168.40	$168.40
Purchase #6	$88.84	11.670%	$99.2076	$99.21	$99.20	$99.20
Purchase #7	$69.39	4.251%	$72.3398	$72.34	$72.35	$72.30
7 purchase totals =	$1,045.38		$1,120.8551	$1,120.86	$1,120.80	$1,120.80