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	$122.94	4.306%	$128.2338	$128.23	$128.25	$128.20
Purchase #2	$155.56	6.789%	$166.121	$166.12	$166.10	$166.10
Purchase #3	$93.51	3.311%	$96.6061	$96.61	$96.60	$96.60
Purchase #4	$147.67	12.317%	$165.8585	$165.86	$165.85	$165.90
Purchase #5	$125.66	6.851%	$134.269	$134.27	$134.25	$134.30
Purchase #6	$166.81	12.328%	$187.3743	$187.37	$187.35	$187.40
Purchase #7	$58.75	5.242%	$61.8297	$61.83	$61.85	$61.80
7 purchase totals =	$870.90		$940.2924	$940.29	$940.25	$940.30