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	$90.53	11.109%	$100.587	$100.59	$100.60	$100.60
Purchase #2	$137.26	3.291%	$141.7772	$141.78	$141.80	$141.80
Purchase #3	$62.58	11.500%	$69.7767	$69.78	$69.80	$69.80
Purchase #4	$30.27	6.828%	$32.3368	$32.34	$32.35	$32.30
Purchase #5	$243.84	5.216%	$256.5587	$256.56	$256.55	$256.60
Purchase #6	$210.81	8.779%	$229.317	$229.32	$229.30	$229.30
Purchase #7	$51.71	7.283%	$55.476	$55.48	$55.50	$55.50
7 purchase totals =	$827.00		$885.8294	$885.85	$885.90	$885.90