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	$229.70	12.829%	$259.1682	$259.17	$259.15	$259.20
Purchase #2	$77.94	10.183%	$85.8766	$85.88	$85.90	$85.90
Purchase #3	$74.32	5.246%	$78.2188	$78.22	$78.20	$78.20
Purchase #4	$215.31	3.198%	$222.1956	$222.20	$222.20	$222.20
Purchase #5	$184.83	4.308%	$192.7925	$192.79	$192.80	$192.80
Purchase #6	$183.88	13.855%	$209.3566	$209.36	$209.35	$209.40
Purchase #7	$129.74	3.489%	$134.2666	$134.27	$134.25	$134.30
7 purchase totals =	$1,095.72		$1,181.8749	$1,181.89	$1,181.85	$1,182.00