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	$145.61	9.720%	$159.7633	$159.76	$159.75	$159.80
Purchase #2	$73.84	5.602%	$77.9765	$77.98	$78.00	$78.00
Purchase #3	$168.53	11.696%	$188.2413	$188.24	$188.25	$188.20
Purchase #4	$235.34	9.727%	$258.2315	$258.23	$258.25	$258.20
Purchase #5	$37.32	9.432%	$40.84	$40.84	$40.85	$40.80
Purchase #6	$140.32	13.253%	$158.9166	$158.92	$158.90	$158.90
Purchase #7	$142.50	12.240%	$159.942	$159.94	$159.95	$159.90
7 purchase totals =	$943.46		$1,043.9112	$1,043.91	$1,043.95	$1,043.80