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	$28.95	13.525%	$32.8655	$32.87	$32.85	$32.90
Purchase #2	$100.47	13.307%	$113.8395	$113.84	$113.85	$113.80
Purchase #3	$54.69	9.506%	$59.8888	$59.89	$59.90	$59.90
Purchase #4	$40.63	11.368%	$45.2488	$45.25	$45.25	$45.20
Purchase #5	$57.56	12.835%	$64.9478	$64.95	$64.95	$64.90
Purchase #6	$65.39	3.617%	$67.7552	$67.76	$67.75	$67.80
Purchase #7	$64.30	10.303%	$70.9248	$70.92	$70.90	$70.90
7 purchase totals =	$411.99		$455.4704	$455.48	$455.45	$455.40