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	$35.79	11.791%	$40.01	$40.01	$40.00	$40.00
Purchase #2	$212.78	13.595%	$241.7074	$241.71	$241.70	$241.70
Purchase #3	$172.60	4.441%	$180.2652	$180.27	$180.25	$180.30
Purchase #4	$163.42	12.689%	$184.1564	$184.16	$184.15	$184.20
Purchase #5	$83.40	11.662%	$93.1261	$93.13	$93.15	$93.10
Purchase #6	$86.79	12.370%	$97.5259	$97.53	$97.55	$97.50
Purchase #7	$90.38	10.137%	$99.5418	$99.54	$99.55	$99.50
7 purchase totals =	$845.16		$936.3328	$936.35	$936.35	$936.30