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	$132.82	8.216%	$143.7325	$143.73	$143.75	$143.70
Purchase #2	$152.25	10.763%	$168.6367	$168.64	$168.65	$168.60
Purchase #3	$143.47	6.302%	$152.5115	$152.51	$152.50	$152.50
Purchase #4	$168.95	7.210%	$181.1313	$181.13	$181.15	$181.10
Purchase #5	$47.39	4.600%	$49.5699	$49.57	$49.55	$49.60
Purchase #6	$140.82	13.507%	$159.8406	$159.84	$159.85	$159.80
Purchase #7	$39.80	13.706%	$45.255	$45.26	$45.25	$45.30
7 purchase totals =	$825.50		$900.6775	$900.68	$900.70	$900.60