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	$28.36	3.373%	$29.3166	$29.32	$29.30	$29.30
Purchase #2	$230.76	4.189%	$240.4265	$240.43	$240.45	$240.40
Purchase #3	$40.51	12.592%	$45.611	$45.61	$45.60	$45.60
Purchase #4	$216.89	13.113%	$245.3308	$245.33	$245.35	$245.30
Purchase #5	$225.83	8.322%	$244.6236	$244.62	$244.60	$244.60
Purchase #6	$136.53	12.785%	$153.9854	$153.99	$154.00	$154.00
Purchase #7	$91.86	4.632%	$96.115	$96.12	$96.10	$96.10
7 purchase totals =	$970.74		$1,055.4089	$1,055.42	$1,055.40	$1,055.30