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	$118.41	8.601%	$128.5944	$128.59	$128.60	$128.60
Purchase #2	$78.28	10.656%	$86.6215	$86.62	$86.60	$86.60
Purchase #3	$23.55	13.441%	$26.7154	$26.72	$26.70	$26.70
Purchase #4	$33.63	9.658%	$36.878	$36.88	$36.90	$36.90
Purchase #5	$33.46	12.473%	$37.6335	$37.63	$37.65	$37.60
Purchase #6	$40.54	9.483%	$44.3844	$44.38	$44.40	$44.40
Purchase #7	$103.73	7.298%	$111.3002	$111.30	$111.30	$111.30
7 purchase totals =	$431.60		$472.1274	$472.12	$472.15	$472.10