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	$50.28	4.417%	$52.5009	$52.50	$52.50	$52.50
Purchase #2	$95.97	3.354%	$99.1888	$99.19	$99.20	$99.20
Purchase #3	$10.37	11.411%	$11.5533	$11.55	$11.55	$11.60
Purchase #4	$92.28	9.271%	$100.8353	$100.84	$100.85	$100.80
Purchase #5	$250.51	11.115%	$278.3542	$278.35	$278.35	$278.40
Purchase #6	$141.36	4.260%	$147.3819	$147.38	$147.40	$147.40
Purchase #7	$159.71	12.627%	$179.8766	$179.88	$179.90	$179.90
7 purchase totals =	$800.48		$869.6910	$869.69	$869.75	$869.80