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	$110.92	4.490%	$115.9003	$115.90	$115.90	$115.90
Purchase #2	$42.29	7.677%	$45.5366	$45.54	$45.55	$45.50
Purchase #3	$26.25	8.824%	$28.5663	$28.57	$28.55	$28.60
Purchase #4	$98.59	4.203%	$102.7337	$102.73	$102.75	$102.70
Purchase #5	$90.35	6.131%	$95.8894	$95.89	$95.90	$95.90
Purchase #6	$70.29	12.197%	$78.8633	$78.86	$78.85	$78.90
Purchase #7	$200.43	6.501%	$213.46	$213.46	$213.45	$213.50
7 purchase totals =	$639.12		$680.9496	$680.95	$680.95	$681.00