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	$168.54	6.393%	$179.3148	$179.31	$179.30	$179.30
Purchase #2	$236.62	8.507%	$256.7493	$256.75	$256.75	$256.70
Purchase #3	$132.88	4.220%	$138.4875	$138.49	$138.50	$138.50
Purchase #4	$219.25	7.240%	$235.1237	$235.12	$235.10	$235.10
Purchase #5	$177.37	13.273%	$200.9123	$200.91	$200.90	$200.90
Purchase #6	$130.63	12.158%	$146.512	$146.51	$146.50	$146.50
Purchase #7	$87.28	12.779%	$98.4335	$98.43	$98.45	$98.40
7 purchase totals =	$1,152.57		$1,255.5331	$1,255.52	$1,255.50	$1,255.40