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	$43.63	4.221%	$45.4716	$45.47	$45.45	$45.50
Purchase #2	$118.90	7.629%	$127.9709	$127.97	$127.95	$128.00
Purchase #3	$59.42	10.633%	$65.7381	$65.74	$65.75	$65.70
Purchase #4	$98.52	12.604%	$110.9375	$110.94	$110.95	$110.90
Purchase #5	$44.88	8.811%	$48.8344	$48.83	$48.85	$48.80
Purchase #6	$131.64	4.663%	$137.7784	$137.78	$137.80	$137.80
Purchase #7	$35.53	10.567%	$39.2845	$39.28	$39.30	$39.30
7 purchase totals =	$532.52		$576.0154	$576.01	$576.05	$576.00