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	$37.28	4.382%	$38.9136	$38.91	$38.90	$38.90
Purchase #2	$30.95	5.782%	$32.7395	$32.74	$32.75	$32.70
Purchase #3	$83.60	7.185%	$89.6067	$89.61	$89.60	$89.60
Purchase #4	$200.40	11.795%	$224.0372	$224.04	$224.05	$224.00
Purchase #5	$226.37	9.298%	$247.4179	$247.42	$247.40	$247.40
Purchase #6	$185.71	13.766%	$211.2748	$211.27	$211.25	$211.30
Purchase #7	$249.93	5.234%	$263.0113	$263.01	$263.00	$263.00
7 purchase totals =	$1,014.24		$1,107.0010	$1,107.00	$1,106.95	$1,106.90