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	$55.38	7.302%	$59.4238	$59.42	$59.40	$59.40
Purchase #2	$216.32	7.397%	$232.3212	$232.32	$232.30	$232.30
Purchase #3	$148.39	12.247%	$166.5633	$166.56	$166.55	$166.60
Purchase #4	$130.71	10.110%	$143.9248	$143.92	$143.90	$143.90
Purchase #5	$38.72	8.240%	$41.9105	$41.91	$41.90	$41.90
Purchase #6	$63.25	10.652%	$69.9874	$69.99	$70.00	$70.00
Purchase #7	$59.69	7.839%	$64.3691	$64.37	$64.35	$64.40
7 purchase totals =	$712.46		$778.5001	$778.49	$778.40	$778.50