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	$93.49	6.600%	$99.6603	$99.66	$99.65	$99.70
Purchase #2	$22.26	9.256%	$24.3204	$24.32	$24.30	$24.30
Purchase #3	$43.72	13.149%	$49.4687	$49.47	$49.45	$49.50
Purchase #4	$140.74	11.364%	$156.7337	$156.73	$156.75	$156.70
Purchase #5	$82.79	13.544%	$94.0031	$94.00	$94.00	$94.00
Purchase #6	$85.78	11.749%	$95.8583	$95.86	$95.85	$95.90
Purchase #7	$53.81	13.639%	$61.1491	$61.15	$61.15	$61.10
7 purchase totals =	$522.59		$581.1936	$581.19	$581.15	$581.20