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	$138.50	6.389%	$147.3488	$147.35	$147.35	$147.30
Purchase #2	$47.86	10.528%	$52.8987	$52.90	$52.90	$52.90
Purchase #3	$37.57	12.495%	$42.2644	$42.26	$42.25	$42.30
Purchase #4	$32.54	7.287%	$34.9112	$34.91	$34.90	$34.90
Purchase #5	$17.32	5.208%	$18.222	$18.22	$18.20	$18.20
Purchase #6	$144.93	8.180%	$156.7853	$156.79	$156.80	$156.80
Purchase #7	$6.34	9.226%	$6.9249	$6.92	$6.90	$6.90
7 purchase totals =	$425.06		$459.3553	$459.35	$459.30	$459.30