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	$188.48	13.431%	$213.7947	$213.79	$213.80	$213.80
Purchase #2	$176.55	10.806%	$195.628	$195.63	$195.65	$195.60
Purchase #3	$237.33	13.714%	$269.8774	$269.88	$269.90	$269.90
Purchase #4	$104.25	4.708%	$109.1581	$109.16	$109.15	$109.20
Purchase #5	$123.50	6.772%	$131.8634	$131.86	$131.85	$131.90
Purchase #6	$184.29	3.531%	$190.7973	$190.80	$190.80	$190.80
Purchase #7	$235.85	8.163%	$255.1024	$255.10	$255.10	$255.10
7 purchase totals =	$1,250.25		$1,366.2213	$1,366.22	$1,366.25	$1,366.30