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	$88.73	12.137%	$99.4992	$99.50	$99.50	$99.50
Purchase #2	$166.29	12.347%	$186.8218	$186.82	$186.80	$186.80
Purchase #3	$228.31	12.772%	$257.4698	$257.47	$257.45	$257.50
Purchase #4	$213.79	9.356%	$233.7922	$233.79	$233.80	$233.80
Purchase #5	$173.66	3.257%	$179.3161	$179.32	$179.30	$179.30
Purchase #6	$101.94	4.498%	$106.5253	$106.53	$106.55	$106.50
Purchase #7	$92.37	11.832%	$103.2992	$103.30	$103.30	$103.30
7 purchase totals =	$1,065.09		$1,166.7236	$1,166.73	$1,166.70	$1,166.70