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	$98.32	6.597%	$104.8062	$104.81	$104.80	$104.80
Purchase #2	$217.28	13.632%	$246.8996	$246.90	$246.90	$246.90
Purchase #3	$205.61	7.624%	$221.2857	$221.29	$221.30	$221.30
Purchase #4	$76.33	12.746%	$86.059	$86.06	$86.05	$86.10
Purchase #5	$139.58	9.265%	$152.5121	$152.51	$152.50	$152.50
Purchase #6	$226.85	9.474%	$248.3418	$248.34	$248.35	$248.30
Purchase #7	$214.83	3.795%	$222.9828	$222.98	$223.00	$223.00
7 purchase totals =	$1,178.80		$1,282.8872	$1,282.89	$1,282.90	$1,282.90