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	$165.85	6.658%	$176.8923	$176.89	$176.90	$176.90
Purchase #2	$70.31	11.627%	$78.4849	$78.48	$78.50	$78.50
Purchase #3	$20.92	8.414%	$22.6802	$22.68	$22.70	$22.70
Purchase #4	$68.55	4.189%	$71.4216	$71.42	$71.40	$71.40
Purchase #5	$177.40	8.109%	$191.7854	$191.79	$191.80	$191.80
Purchase #6	$75.29	4.641%	$78.7842	$78.78	$78.80	$78.80
Purchase #7	$164.57	12.283%	$184.7841	$184.78	$184.80	$184.80
7 purchase totals =	$742.89		$804.8327	$804.82	$804.90	$804.90