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	$37.65	7.149%	$40.3416	$40.34	$40.35	$40.30
Purchase #2	$32.96	11.439%	$36.7303	$36.73	$36.75	$36.70
Purchase #3	$173.71	9.868%	$190.8517	$190.85	$190.85	$190.90
Purchase #4	$100.41	11.534%	$111.9913	$111.99	$112.00	$112.00
Purchase #5	$202.90	3.704%	$210.4154	$210.42	$210.40	$210.40
Purchase #6	$218.83	10.206%	$241.1638	$241.16	$241.15	$241.20
Purchase #7	$42.88	5.710%	$45.3284	$45.33	$45.35	$45.30
7 purchase totals =	$809.34		$876.8225	$876.82	$876.85	$876.80