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	$140.89	3.186%	$145.3788	$145.38	$145.40	$145.40
Purchase #2	$220.86	11.306%	$245.8304	$245.83	$245.85	$245.80
Purchase #3	$219.95	11.498%	$245.2399	$245.24	$245.25	$245.20
Purchase #4	$154.38	5.553%	$162.9527	$162.95	$162.95	$163.00
Purchase #5	$60.66	3.193%	$62.5969	$62.60	$62.60	$62.60
Purchase #6	$119.51	9.616%	$131.0021	$131.00	$131.00	$131.00
Purchase #7	$74.49	10.693%	$82.4552	$82.46	$82.45	$82.50
7 purchase totals =	$990.74		$1,075.4560	$1,075.46	$1,075.50	$1,075.50