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	$59.82	12.622%	$67.3705	$67.37	$67.35	$67.40
Purchase #2	$197.69	12.809%	$223.0121	$223.01	$223.00	$223.00
Purchase #3	$93.98	4.609%	$98.3115	$98.31	$98.30	$98.30
Purchase #4	$143.68	3.195%	$148.2706	$148.27	$148.25	$148.30
Purchase #5	$68.48	8.720%	$74.4515	$74.45	$74.45	$74.50
Purchase #6	$188.62	5.240%	$198.5037	$198.50	$198.50	$198.50
Purchase #7	$40.75	3.104%	$42.0149	$42.01	$42.00	$42.00
7 purchase totals =	$793.02		$851.9348	$851.92	$851.85	$852.00