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	$90.42	10.381%	$99.8065	$99.81	$99.80	$99.80
Purchase #2	$82.47	4.729%	$86.37	$86.37	$86.35	$86.40
Purchase #3	$136.77	3.329%	$141.3231	$141.32	$141.30	$141.30
Purchase #4	$230.28	10.818%	$255.1917	$255.19	$255.20	$255.20
Purchase #5	$204.48	4.291%	$213.2542	$213.25	$213.25	$213.30
Purchase #6	$233.72	11.386%	$260.3314	$260.33	$260.35	$260.30
Purchase #7	$231.95	11.784%	$259.283	$259.28	$259.30	$259.30
7 purchase totals =	$1,210.09		$1,315.5599	$1,315.55	$1,315.55	$1,315.60