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	$72.64	8.273%	$78.6495	$78.65	$78.65	$78.60
Purchase #2	$98.25	13.459%	$111.4735	$111.47	$111.45	$111.50
Purchase #3	$233.77	3.337%	$241.5709	$241.57	$241.55	$241.60
Purchase #4	$156.30	12.319%	$175.5546	$175.55	$175.55	$175.60
Purchase #5	$167.40	6.416%	$178.1404	$178.14	$178.15	$178.10
Purchase #6	$17.94	10.270%	$19.7824	$19.78	$19.80	$19.80
Purchase #7	$116.46	12.248%	$130.724	$130.72	$130.70	$130.70
7 purchase totals =	$862.76		$935.8953	$935.88	$935.85	$935.90