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	$238.58	12.691%	$268.8582	$268.86	$268.85	$268.90
Purchase #2	$231.43	6.642%	$246.8016	$246.80	$246.80	$246.80
Purchase #3	$176.85	13.533%	$200.7831	$200.78	$200.80	$200.80
Purchase #4	$57.74	12.428%	$64.9159	$64.92	$64.90	$64.90
Purchase #5	$143.36	6.243%	$152.31	$152.31	$152.30	$152.30
Purchase #6	$98.35	11.346%	$109.5088	$109.51	$109.50	$109.50
Purchase #7	$183.58	7.297%	$196.9758	$196.98	$197.00	$197.00
7 purchase totals =	$1,129.89		$1,240.1534	$1,240.16	$1,240.15	$1,240.20