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	$105.78	7.668%	$113.8912	$113.89	$113.90	$113.90
Purchase #2	$65.70	8.163%	$71.0631	$71.06	$71.05	$71.10
Purchase #3	$127.26	10.665%	$140.8323	$140.83	$140.85	$140.80
Purchase #4	$39.33	12.209%	$44.1318	$44.13	$44.15	$44.10
Purchase #5	$125.73	11.614%	$140.3323	$140.33	$140.35	$140.30
Purchase #6	$34.35	7.627%	$36.9699	$36.97	$36.95	$37.00
Purchase #7	$37.78	5.123%	$39.7155	$39.72	$39.70	$39.70
7 purchase totals =	$535.93		$586.9361	$586.93	$586.95	$586.90