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	$137.76	3.436%	$142.4934	$142.49	$142.50	$142.50
Purchase #2	$9.59	13.427%	$10.8776	$10.88	$10.90	$10.90
Purchase #3	$225.25	10.853%	$249.6964	$249.70	$249.70	$249.70
Purchase #4	$90.35	7.278%	$96.9257	$96.93	$96.95	$96.90
Purchase #5	$32.51	13.502%	$36.8995	$36.90	$36.90	$36.90
Purchase #6	$80.75	10.147%	$88.9437	$88.94	$88.95	$88.90
Purchase #7	$73.95	5.755%	$78.2058	$78.21	$78.20	$78.20
7 purchase totals =	$650.16		$704.0421	$704.05	$704.10	$704.00