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	$12.77	6.349%	$13.5808	$13.58	$13.60	$13.60
Purchase #2	$147.71	3.463%	$152.8252	$152.83	$152.85	$152.80
Purchase #3	$83.26	10.187%	$91.7417	$91.74	$91.75	$91.70
Purchase #4	$91.91	10.858%	$101.8896	$101.89	$101.90	$101.90
Purchase #5	$89.59	10.772%	$99.2406	$99.24	$99.25	$99.20
Purchase #6	$15.61	9.871%	$17.1509	$17.15	$17.15	$17.20
Purchase #7	$102.84	8.336%	$111.4127	$111.41	$111.40	$111.40
7 purchase totals =	$543.69		$587.8415	$587.84	$587.90	$587.80