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	$34.84	7.764%	$37.545	$37.55	$37.55	$37.50
Purchase #2	$86.68	3.156%	$89.4156	$89.42	$89.40	$89.40
Purchase #3	$131.67	6.514%	$140.247	$140.25	$140.25	$140.20
Purchase #4	$64.35	5.570%	$67.9343	$67.93	$67.95	$67.90
Purchase #5	$158.89	4.751%	$166.4389	$166.44	$166.45	$166.40
Purchase #6	$156.71	7.576%	$168.5823	$168.58	$168.60	$168.60
Purchase #7	$240.38	5.522%	$253.6538	$253.65	$253.65	$253.70
7 purchase totals =	$873.52		$923.8169	$923.82	$923.85	$923.70