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	$31.60	7.243%	$33.8888	$33.89	$33.90	$33.90
Purchase #2	$131.48	9.243%	$143.6327	$143.63	$143.65	$143.60
Purchase #3	$181.98	12.401%	$204.5473	$204.55	$204.55	$204.50
Purchase #4	$93.26	6.136%	$98.9824	$98.98	$99.00	$99.00
Purchase #5	$196.85	12.828%	$222.1019	$222.10	$222.10	$222.10
Purchase #6	$126.27	8.610%	$137.1418	$137.14	$137.15	$137.10
Purchase #7	$54.85	8.848%	$59.7031	$59.70	$59.70	$59.70
7 purchase totals =	$816.29		$899.9980	$899.99	$900.05	$899.90