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	$111.78	3.102%	$115.2474	$115.25	$115.25	$115.20
Purchase #2	$89.58	11.452%	$99.8387	$99.84	$99.85	$99.80
Purchase #3	$248.61	10.757%	$275.353	$275.35	$275.35	$275.40
Purchase #4	$68.97	13.107%	$78.0099	$78.01	$78.00	$78.00
Purchase #5	$184.82	6.442%	$196.7261	$196.73	$196.75	$196.70
Purchase #6	$43.35	7.867%	$46.7603	$46.76	$46.75	$46.80
Purchase #7	$17.35	5.716%	$18.3417	$18.34	$18.35	$18.30
7 purchase totals =	$764.46		$830.2771	$830.28	$830.30	$830.20