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	$28.64	13.665%	$32.5537	$32.55	$32.55	$32.60
Purchase #2	$91.83	4.827%	$96.2626	$96.26	$96.25	$96.30
Purchase #3	$233.27	12.667%	$262.8183	$262.82	$262.80	$262.80
Purchase #4	$95.48	9.108%	$104.1763	$104.18	$104.20	$104.20
Purchase #5	$100.78	6.311%	$107.1402	$107.14	$107.15	$107.10
Purchase #6	$124.28	8.508%	$134.8537	$134.85	$134.85	$134.90
Purchase #7	$55.29	12.317%	$62.1001	$62.10	$62.10	$62.10
7 purchase totals =	$729.57		$799.9049	$799.90	$799.90	$800.00