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	$74.67	8.210%	$80.8004	$80.80	$80.80	$80.80
Purchase #2	$175.54	6.385%	$186.7482	$186.75	$186.75	$186.70
Purchase #3	$228.53	13.323%	$258.9771	$258.98	$259.00	$259.00
Purchase #4	$171.90	4.233%	$179.1765	$179.18	$179.20	$179.20
Purchase #5	$95.92	11.367%	$106.8232	$106.82	$106.80	$106.80
Purchase #6	$40.69	12.284%	$45.6884	$45.69	$45.70	$45.70
Purchase #7	$236.31	7.365%	$253.7142	$253.71	$253.70	$253.70
7 purchase totals =	$1,023.56		$1,111.9280	$1,111.93	$1,111.95	$1,111.90