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	$78.85	10.835%	$87.3934	$87.39	$87.40	$87.40
Purchase #2	$181.29	3.297%	$187.2671	$187.27	$187.25	$187.30
Purchase #3	$122.49	11.700%	$136.8213	$136.82	$136.80	$136.80
Purchase #4	$73.70	9.152%	$80.445	$80.45	$80.45	$80.40
Purchase #5	$180.82	5.873%	$191.4396	$191.44	$191.45	$191.40
Purchase #6	$22.91	6.795%	$24.4667	$24.47	$24.45	$24.50
Purchase #7	$92.32	12.351%	$103.7224	$103.72	$103.70	$103.70
7 purchase totals =	$752.38		$811.5555	$811.56	$811.50	$811.50