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	$88.73	12.576%	$99.8887	$99.89	$99.90	$99.90
Purchase #2	$94.36	9.168%	$103.0109	$103.01	$103.00	$103.00
Purchase #3	$40.59	10.515%	$44.858	$44.86	$44.85	$44.90
Purchase #4	$174.64	12.608%	$196.6586	$196.66	$196.65	$196.70
Purchase #5	$146.49	4.561%	$153.1714	$153.17	$153.15	$153.20
Purchase #6	$198.81	8.576%	$215.8599	$215.86	$215.85	$215.90
Purchase #7	$239.85	10.556%	$265.1686	$265.17	$265.15	$265.20
7 purchase totals =	$983.47		$1,078.6161	$1,078.62	$1,078.55	$1,078.80