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	$96.40	7.346%	$103.4815	$103.48	$103.50	$103.50
Purchase #2	$11.44	9.295%	$12.5033	$12.50	$12.50	$12.50
Purchase #3	$96.97	3.375%	$100.2427	$100.24	$100.25	$100.20
Purchase #4	$121.89	7.874%	$131.4876	$131.49	$131.50	$131.50
Purchase #5	$142.80	9.329%	$156.1218	$156.12	$156.10	$156.10
Purchase #6	$54.44	6.867%	$58.1784	$58.18	$58.20	$58.20
Purchase #7	$59.58	12.371%	$66.9506	$66.95	$66.95	$67.00
7 purchase totals =	$583.52		$628.9659	$628.96	$629.00	$629.00