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	$65.41	11.777%	$73.1133	$73.11	$73.10	$73.10
Purchase #2	$174.52	12.602%	$196.513	$196.51	$196.50	$196.50
Purchase #3	$103.74	5.302%	$109.2403	$109.24	$109.25	$109.20
Purchase #4	$227.50	5.848%	$240.8042	$240.80	$240.80	$240.80
Purchase #5	$170.48	9.445%	$186.5818	$186.58	$186.60	$186.60
Purchase #6	$127.93	13.695%	$145.45	$145.45	$145.45	$145.50
Purchase #7	$77.38	12.804%	$87.2877	$87.29	$87.30	$87.30
7 purchase totals =	$946.96		$1,038.9903	$1,038.98	$1,039.00	$1,039.00