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	$122.50	5.112%	$128.7622	$128.76	$128.75	$128.80
Purchase #2	$176.50	3.358%	$182.4269	$182.43	$182.45	$182.40
Purchase #3	$240.69	13.307%	$272.7186	$272.72	$272.70	$272.70
Purchase #4	$81.68	5.613%	$86.2647	$86.26	$86.25	$86.30
Purchase #5	$150.95	11.620%	$168.4904	$168.49	$168.50	$168.50
Purchase #6	$240.44	9.139%	$262.4138	$262.41	$262.40	$262.40
Purchase #7	$77.77	5.297%	$81.8895	$81.89	$81.90	$81.90
7 purchase totals =	$1,090.53		$1,182.9661	$1,182.96	$1,182.95	$1,183.00