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	$33.93	9.371%	$37.1096	$37.11	$37.10	$37.10
Purchase #2	$138.92	12.380%	$156.1183	$156.12	$156.10	$156.10
Purchase #3	$113.67	8.563%	$123.4036	$123.40	$123.40	$123.40
Purchase #4	$183.95	9.234%	$200.9359	$200.94	$200.95	$200.90
Purchase #5	$45.54	4.503%	$47.5907	$47.59	$47.60	$47.60
Purchase #6	$47.30	6.674%	$50.4568	$50.46	$50.45	$50.50
Purchase #7	$156.69	6.453%	$166.8012	$166.80	$166.80	$166.80
7 purchase totals =	$720.00		$782.4161	$782.42	$782.40	$782.40