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	$27.70	12.685%	$31.2137	$31.21	$31.20	$31.20
Purchase #2	$185.72	7.711%	$200.0409	$200.04	$200.05	$200.00
Purchase #3	$9.76	5.130%	$10.2607	$10.26	$10.25	$10.30
Purchase #4	$35.80	6.833%	$38.2462	$38.25	$38.25	$38.20
Purchase #5	$92.65	7.306%	$99.419	$99.42	$99.40	$99.40
Purchase #6	$92.55	13.651%	$105.184	$105.18	$105.20	$105.20
Purchase #7	$183.37	9.573%	$200.924	$200.92	$200.90	$200.90
7 purchase totals =	$627.55		$685.2885	$685.28	$685.25	$685.20