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	$107.92	3.465%	$111.6594	$111.66	$111.65	$111.70
Purchase #2	$144.38	9.172%	$157.6225	$157.62	$157.60	$157.60
Purchase #3	$86.26	11.426%	$96.1161	$96.12	$96.10	$96.10
Purchase #4	$127.86	8.805%	$139.1181	$139.12	$139.10	$139.10
Purchase #5	$94.46	7.760%	$101.7901	$101.79	$101.80	$101.80
Purchase #6	$18.90	13.477%	$21.4472	$21.45	$21.45	$21.40
Purchase #7	$39.77	12.263%	$44.647	$44.65	$44.65	$44.60
7 purchase totals =	$619.55		$672.4004	$672.41	$672.35	$672.30