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	$45.71	13.150%	$51.7209	$51.72	$51.70	$51.70
Purchase #2	$177.89	7.858%	$191.8686	$191.87	$191.85	$191.90
Purchase #3	$88.62	7.124%	$94.9333	$94.93	$94.95	$94.90
Purchase #4	$29.97	8.471%	$32.5088	$32.51	$32.50	$32.50
Purchase #5	$58.49	8.170%	$63.2686	$63.27	$63.25	$63.30
Purchase #6	$208.80	6.531%	$222.4367	$222.44	$222.45	$222.40
Purchase #7	$189.62	11.678%	$211.7638	$211.76	$211.75	$211.80
7 purchase totals =	$799.10		$868.5007	$868.50	$868.45	$868.50