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	$60.37	12.279%	$67.7828	$67.78	$67.80	$67.80
Purchase #2	$157.40	13.752%	$179.0456	$179.05	$179.05	$179.00
Purchase #3	$74.34	7.689%	$80.056	$80.06	$80.05	$80.10
Purchase #4	$132.71	9.769%	$145.6744	$145.67	$145.65	$145.70
Purchase #5	$115.43	11.307%	$128.4817	$128.48	$128.50	$128.50
Purchase #6	$94.88	4.167%	$98.8336	$98.83	$98.85	$98.80
Purchase #7	$84.33	6.484%	$89.798	$89.80	$89.80	$89.80
7 purchase totals =	$719.46		$789.6721	$789.67	$789.70	$789.70