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	$105.63	6.797%	$112.8097	$112.81	$112.80	$112.80
Purchase #2	$139.83	11.861%	$156.4152	$156.42	$156.40	$156.40
Purchase #3	$87.27	4.217%	$90.9502	$90.95	$90.95	$91.00
Purchase #4	$128.99	6.525%	$137.4066	$137.41	$137.40	$137.40
Purchase #5	$237.68	11.520%	$265.0607	$265.06	$265.05	$265.10
Purchase #6	$141.88	13.322%	$160.7813	$160.78	$160.80	$160.80
Purchase #7	$37.79	6.638%	$40.2985	$40.30	$40.30	$40.30
7 purchase totals =	$879.07		$963.7222	$963.73	$963.70	$963.80