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	$52.63	6.191%	$55.8883	$55.89	$55.90	$55.90
Purchase #2	$60.81	7.799%	$65.5526	$65.55	$65.55	$65.60
Purchase #3	$205.67	8.181%	$222.4959	$222.50	$222.50	$222.50
Purchase #4	$162.95	8.328%	$176.5205	$176.52	$176.50	$176.50
Purchase #5	$179.83	10.576%	$198.8488	$198.85	$198.85	$198.80
Purchase #6	$81.43	10.266%	$89.7896	$89.79	$89.80	$89.80
Purchase #7	$67.70	3.722%	$70.2198	$70.22	$70.20	$70.20
7 purchase totals =	$811.02		$879.3155	$879.32	$879.30	$879.30