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	$41.41	3.609%	$42.9045	$42.90	$42.90	$42.90
Purchase #2	$18.79	13.220%	$21.274	$21.27	$21.25	$21.30
Purchase #3	$192.80	12.454%	$216.8113	$216.81	$216.80	$216.80
Purchase #4	$165.62	4.434%	$172.9636	$172.96	$172.95	$173.00
Purchase #5	$80.29	3.554%	$83.1435	$83.14	$83.15	$83.10
Purchase #6	$139.32	3.603%	$144.3397	$144.34	$144.35	$144.30
Purchase #7	$26.53	3.430%	$27.44	$27.44	$27.45	$27.40
7 purchase totals =	$664.76		$708.8766	$708.86	$708.85	$708.80