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	$137.73	5.236%	$144.9415	$144.94	$144.95	$144.90
Purchase #2	$59.58	11.309%	$66.3179	$66.32	$66.30	$66.30
Purchase #3	$119.59	11.647%	$133.5186	$133.52	$133.50	$133.50
Purchase #4	$162.76	10.526%	$179.8921	$179.89	$179.90	$179.90
Purchase #5	$120.86	7.381%	$129.7807	$129.78	$129.80	$129.80
Purchase #6	$110.87	3.351%	$114.5853	$114.59	$114.60	$114.60
Purchase #7	$36.63	8.703%	$39.8179	$39.82	$39.80	$39.80
7 purchase totals =	$748.02		$808.8540	$808.86	$808.85	$808.80