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	$109.64	7.806%	$118.1985	$118.20	$118.20	$118.20
Purchase #2	$164.93	12.608%	$185.7244	$185.72	$185.70	$185.70
Purchase #3	$130.81	12.381%	$147.0056	$147.01	$147.00	$147.00
Purchase #4	$104.65	11.699%	$116.893	$116.89	$116.90	$116.90
Purchase #5	$154.48	6.560%	$164.6139	$164.61	$164.60	$164.60
Purchase #6	$131.98	3.469%	$136.5584	$136.56	$136.55	$136.60
Purchase #7	$45.44	9.148%	$49.5969	$49.60	$49.60	$49.60
7 purchase totals =	$841.93		$918.5907	$918.59	$918.55	$918.60