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	$131.38	6.144%	$139.452	$139.45	$139.45	$139.50
Purchase #2	$192.42	12.844%	$217.1344	$217.13	$217.15	$217.10
Purchase #3	$19.35	8.562%	$21.0067	$21.01	$21.00	$21.00
Purchase #4	$151.56	13.348%	$171.7902	$171.79	$171.80	$171.80
Purchase #5	$94.92	9.488%	$103.926	$103.93	$103.95	$103.90
Purchase #6	$179.32	4.232%	$186.9088	$186.91	$186.90	$186.90
Purchase #7	$238.49	13.607%	$270.9413	$270.94	$270.95	$270.90
7 purchase totals =	$1,007.44		$1,111.1594	$1,111.16	$1,111.20	$1,111.10