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	$138.66	6.453%	$147.6077	$147.61	$147.60	$147.60
Purchase #2	$50.32	12.192%	$56.455	$56.46	$56.45	$56.50
Purchase #3	$64.62	4.320%	$67.4116	$67.41	$67.40	$67.40
Purchase #4	$145.89	6.851%	$155.8849	$155.88	$155.90	$155.90
Purchase #5	$157.93	11.453%	$176.0177	$176.02	$176.00	$176.00
Purchase #6	$38.56	9.777%	$42.33	$42.33	$42.35	$42.30
Purchase #7	$54.75	3.841%	$56.8529	$56.85	$56.85	$56.90
7 purchase totals =	$650.73		$702.5598	$702.56	$702.55	$702.60