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	$166.44	13.273%	$188.5316	$188.53	$188.55	$188.50
Purchase #2	$58.46	13.564%	$66.3895	$66.39	$66.40	$66.40
Purchase #3	$101.89	6.550%	$108.5638	$108.56	$108.55	$108.60
Purchase #4	$20.93	7.293%	$22.4564	$22.46	$22.45	$22.50
Purchase #5	$118.30	4.376%	$123.4768	$123.48	$123.50	$123.50
Purchase #6	$23.55	4.269%	$24.5553	$24.56	$24.55	$24.60
Purchase #7	$126.94	7.795%	$136.835	$136.84	$136.85	$136.80
7 purchase totals =	$616.51		$670.8084	$670.82	$670.85	$670.90