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	$238.32	11.710%	$266.2273	$266.23	$266.25	$266.20
Purchase #2	$17.80	5.783%	$18.8294	$18.83	$18.85	$18.80
Purchase #3	$143.88	3.791%	$149.3345	$149.33	$149.35	$149.30
Purchase #4	$54.66	5.156%	$57.4783	$57.48	$57.50	$57.50
Purchase #5	$78.97	8.225%	$85.4653	$85.47	$85.45	$85.50
Purchase #6	$45.30	5.712%	$47.8875	$47.89	$47.90	$47.90
Purchase #7	$67.50	5.353%	$71.1133	$71.11	$71.10	$71.10
7 purchase totals =	$646.43		$696.3356	$696.34	$696.40	$696.30