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	$65.82	7.109%	$70.4991	$70.50	$70.50	$70.50
Purchase #2	$70.61	12.201%	$79.2251	$79.23	$79.25	$79.20
Purchase #3	$77.39	10.354%	$85.403	$85.40	$85.40	$85.40
Purchase #4	$149.47	4.297%	$155.8927	$155.89	$155.90	$155.90
Purchase #5	$18.60	4.811%	$19.4948	$19.49	$19.50	$19.50
Purchase #6	$67.50	6.446%	$71.8511	$71.85	$71.85	$71.90
Purchase #7	$41.42	8.602%	$44.9829	$44.98	$45.00	$45.00
7 purchase totals =	$490.81		$527.3487	$527.34	$527.40	$527.40