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	$26.60	10.488%	$29.3898	$29.39	$29.40	$29.40
Purchase #2	$53.28	12.464%	$59.9208	$59.92	$59.90	$59.90
Purchase #3	$90.55	12.570%	$101.9321	$101.93	$101.95	$101.90
Purchase #4	$27.48	11.829%	$30.7306	$30.73	$30.75	$30.70
Purchase #5	$94.43	11.458%	$105.2498	$105.25	$105.25	$105.20
Purchase #6	$103.32	10.822%	$114.5013	$114.50	$114.50	$114.50
Purchase #7	$35.56	12.850%	$40.1295	$40.13	$40.15	$40.10
7 purchase totals =	$431.22		$481.8539	$481.85	$481.90	$481.70