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	$9.66	4.706%	$10.1146	$10.11	$10.10	$10.10
Purchase #2	$146.60	5.632%	$154.8565	$154.86	$154.85	$154.90
Purchase #3	$198.63	10.591%	$219.6669	$219.67	$219.65	$219.70
Purchase #4	$46.37	10.218%	$51.1081	$51.11	$51.10	$51.10
Purchase #5	$97.72	10.569%	$108.048	$108.05	$108.05	$108.00
Purchase #6	$90.89	12.103%	$101.8904	$101.89	$101.90	$101.90
Purchase #7	$30.56	6.645%	$32.5907	$32.59	$32.60	$32.60
7 purchase totals =	$620.43		$678.2752	$678.28	$678.25	$678.30