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	$249.32	9.381%	$272.7087	$272.71	$272.70	$272.70
Purchase #2	$36.41	13.765%	$41.4218	$41.42	$41.40	$41.40
Purchase #3	$40.51	3.393%	$41.8845	$41.88	$41.90	$41.90
Purchase #4	$154.42	12.254%	$173.3426	$173.34	$173.35	$173.30
Purchase #5	$33.69	10.775%	$37.3201	$37.32	$37.30	$37.30
Purchase #6	$204.52	12.155%	$229.3794	$229.38	$229.40	$229.40
Purchase #7	$203.91	10.143%	$224.5926	$224.59	$224.60	$224.60
7 purchase totals =	$922.78		$1,020.6497	$1,020.64	$1,020.65	$1,020.60