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	$34.52	13.385%	$39.1405	$39.14	$39.15	$39.10
Purchase #2	$237.35	7.162%	$254.349	$254.35	$254.35	$254.30
Purchase #3	$30.92	4.311%	$32.253	$32.25	$32.25	$32.30
Purchase #4	$238.60	12.546%	$268.5348	$268.53	$268.55	$268.50
Purchase #5	$80.45	6.410%	$85.6068	$85.61	$85.60	$85.60
Purchase #6	$238.66	13.433%	$270.7192	$270.72	$270.70	$270.70
Purchase #7	$177.33	13.864%	$201.915	$201.92	$201.90	$201.90
7 purchase totals =	$1,037.83		$1,152.5183	$1,152.52	$1,152.50	$1,152.40