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	$95.70	13.247%	$108.3774	$108.38	$108.40	$108.40
Purchase #2	$131.63	7.848%	$141.9603	$141.96	$141.95	$142.00
Purchase #3	$159.80	5.218%	$168.1384	$168.14	$168.15	$168.10
Purchase #4	$25.47	9.565%	$27.9062	$27.91	$27.90	$27.90
Purchase #5	$124.44	13.490%	$141.227	$141.23	$141.25	$141.20
Purchase #6	$125.98	9.479%	$137.9216	$137.92	$137.90	$137.90
Purchase #7	$178.76	6.798%	$190.9121	$190.91	$190.90	$190.90
7 purchase totals =	$841.78		$916.4430	$916.45	$916.45	$916.40