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	$86.89	4.163%	$90.5072	$90.51	$90.50	$90.50
Purchase #2	$46.60	7.829%	$50.2483	$50.25	$50.25	$50.20
Purchase #3	$167.49	7.229%	$179.5979	$179.60	$179.60	$179.60
Purchase #4	$234.64	4.864%	$246.0529	$246.05	$246.05	$246.10
Purchase #5	$69.77	3.208%	$72.0082	$72.01	$72.00	$72.00
Purchase #6	$57.96	6.308%	$61.6161	$61.62	$61.60	$61.60
Purchase #7	$52.59	12.137%	$58.9728	$58.97	$58.95	$59.00
7 purchase totals =	$715.94		$759.0034	$759.01	$758.95	$759.00