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	$31.47	13.748%	$35.7965	$35.80	$35.80	$35.80
Purchase #2	$204.88	5.386%	$215.9148	$215.91	$215.90	$215.90
Purchase #3	$141.59	6.315%	$150.5314	$150.53	$150.55	$150.50
Purchase #4	$114.89	10.405%	$126.8443	$126.84	$126.85	$126.80
Purchase #5	$136.80	3.144%	$141.101	$141.10	$141.10	$141.10
Purchase #6	$152.94	4.328%	$159.5592	$159.56	$159.55	$159.60
Purchase #7	$18.93	13.260%	$21.4401	$21.44	$21.45	$21.40
7 purchase totals =	$801.50		$851.1873	$851.18	$851.20	$851.10