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	$36.39	9.818%	$39.9628	$39.96	$39.95	$40.00
Purchase #2	$168.87	9.849%	$185.502	$185.50	$185.50	$185.50
Purchase #3	$33.88	6.302%	$36.0151	$36.02	$36.00	$36.00
Purchase #4	$155.54	7.178%	$166.7047	$166.70	$166.70	$166.70
Purchase #5	$228.90	6.323%	$243.3733	$243.37	$243.35	$243.40
Purchase #6	$147.90	12.653%	$166.6138	$166.61	$166.60	$166.60
Purchase #7	$33.73	12.433%	$37.9237	$37.92	$37.90	$37.90
7 purchase totals =	$805.21		$876.0954	$876.08	$876.00	$876.10