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	$120.61	6.836%	$128.8549	$128.85	$128.85	$128.90
Purchase #2	$207.90	9.833%	$228.3428	$228.34	$228.35	$228.30
Purchase #3	$210.82	8.256%	$228.2253	$228.23	$228.25	$228.20
Purchase #4	$111.53	10.802%	$123.5775	$123.58	$123.60	$123.60
Purchase #5	$170.35	7.392%	$182.9423	$182.94	$182.95	$182.90
Purchase #6	$39.33	5.482%	$41.4861	$41.49	$41.50	$41.50
Purchase #7	$148.47	3.516%	$153.6902	$153.69	$153.70	$153.70
7 purchase totals =	$1,009.01		$1,087.1191	$1,087.12	$1,087.20	$1,087.10