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	$64.50	12.237%	$72.3929	$72.39	$72.40	$72.40
Purchase #2	$178.75	5.327%	$188.272	$188.27	$188.25	$188.30
Purchase #3	$50.34	13.521%	$57.1465	$57.15	$57.15	$57.10
Purchase #4	$224.76	7.334%	$241.2439	$241.24	$241.25	$241.20
Purchase #5	$6.82	10.587%	$7.542	$7.54	$7.55	$7.50
Purchase #6	$172.46	10.647%	$190.8218	$190.82	$190.80	$190.80
Purchase #7	$69.34	6.324%	$73.7251	$73.73	$73.75	$73.70
7 purchase totals =	$766.97		$831.1442	$831.14	$831.15	$831.00