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	$22.59	13.171%	$25.5653	$25.57	$25.55	$25.60
Purchase #2	$102.45	7.175%	$109.8008	$109.80	$109.80	$109.80
Purchase #3	$180.51	4.237%	$188.1582	$188.16	$188.15	$188.20
Purchase #4	$140.72	7.250%	$150.9222	$150.92	$150.90	$150.90
Purchase #5	$233.74	8.462%	$253.5191	$253.52	$253.50	$253.50
Purchase #6	$25.55	7.532%	$27.4744	$27.47	$27.45	$27.50
Purchase #7	$77.48	8.336%	$83.9387	$83.94	$83.95	$83.90
7 purchase totals =	$783.04		$839.3787	$839.38	$839.30	$839.40