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	$96.32	4.306%	$100.4675	$100.47	$100.45	$100.50
Purchase #2	$73.94	10.360%	$81.6002	$81.60	$81.60	$81.60
Purchase #3	$45.69	6.316%	$48.5758	$48.58	$48.60	$48.60
Purchase #4	$217.30	12.432%	$244.3147	$244.31	$244.30	$244.30
Purchase #5	$101.86	11.192%	$113.2602	$113.26	$113.25	$113.30
Purchase #6	$216.46	6.407%	$230.3286	$230.33	$230.35	$230.30
Purchase #7	$74.68	4.756%	$78.2318	$78.23	$78.25	$78.20
7 purchase totals =	$826.25		$896.7788	$896.78	$896.80	$896.80