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	$29.81	11.220%	$33.1547	$33.15	$33.15	$33.20
Purchase #2	$133.84	3.814%	$138.9447	$138.94	$138.95	$138.90
Purchase #3	$32.83	4.738%	$34.3855	$34.39	$34.40	$34.40
Purchase #4	$199.61	11.293%	$222.152	$222.15	$222.15	$222.20
Purchase #5	$211.80	3.372%	$218.9419	$218.94	$218.95	$218.90
Purchase #6	$182.73	4.448%	$190.8578	$190.86	$190.85	$190.90
Purchase #7	$146.25	3.367%	$151.1742	$151.17	$151.15	$151.20
7 purchase totals =	$936.87		$989.6108	$989.60	$989.60	$989.70