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	$29.83	13.678%	$33.9101	$33.91	$33.90	$33.90
Purchase #2	$130.80	11.809%	$146.2462	$146.25	$146.25	$146.20
Purchase #3	$29.57	9.530%	$32.388	$32.39	$32.40	$32.40
Purchase #4	$220.84	7.234%	$236.8156	$236.82	$236.80	$236.80
Purchase #5	$94.43	12.682%	$106.4056	$106.41	$106.40	$106.40
Purchase #6	$62.82	3.562%	$65.0576	$65.06	$65.05	$65.10
Purchase #7	$112.67	9.728%	$123.6305	$123.63	$123.65	$123.60
7 purchase totals =	$680.96		$744.4536	$744.47	$744.45	$744.40