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	$150.59	10.103%	$165.8041	$165.80	$165.80	$165.80
Purchase #2	$208.77	13.181%	$236.288	$236.29	$236.30	$236.30
Purchase #3	$137.79	11.373%	$153.4609	$153.46	$153.45	$153.50
Purchase #4	$37.26	11.351%	$41.4894	$41.49	$41.50	$41.50
Purchase #5	$119.95	12.498%	$134.9414	$134.94	$134.95	$134.90
Purchase #6	$190.83	10.567%	$210.995	$211.00	$211.00	$211.00
Purchase #7	$131.82	4.595%	$137.8771	$137.88	$137.90	$137.90
7 purchase totals =	$977.01		$1,080.8559	$1,080.86	$1,080.90	$1,080.90