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	$250.72	8.679%	$272.48	$272.48	$272.50	$272.50
Purchase #2	$171.55	11.414%	$191.1307	$191.13	$191.15	$191.10
Purchase #3	$27.47	8.618%	$29.8374	$29.84	$29.85	$29.80
Purchase #4	$8.31	13.535%	$9.4348	$9.43	$9.45	$9.40
Purchase #5	$209.85	6.249%	$222.9635	$222.96	$222.95	$223.00
Purchase #6	$37.27	12.718%	$42.01	$42.01	$42.00	$42.00
Purchase #7	$103.84	5.114%	$109.1504	$109.15	$109.15	$109.20
7 purchase totals =	$809.01		$877.0068	$877.00	$877.05	$877.00