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	$152.50	13.758%	$173.481	$173.48	$173.50	$173.50
Purchase #2	$243.75	10.422%	$269.1536	$269.15	$269.15	$269.20
Purchase #3	$105.74	3.255%	$109.1818	$109.18	$109.20	$109.20
Purchase #4	$250.63	5.826%	$265.2317	$265.23	$265.25	$265.20
Purchase #5	$51.72	6.632%	$55.1501	$55.15	$55.15	$55.20
Purchase #6	$172.49	10.165%	$190.0236	$190.02	$190.00	$190.00
Purchase #7	$138.48	13.311%	$156.9131	$156.91	$156.90	$156.90
7 purchase totals =	$1,115.31		$1,219.1349	$1,219.12	$1,219.15	$1,219.20