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	$68.88	3.215%	$71.0945	$71.09	$71.10	$71.10
Purchase #2	$106.43	12.743%	$119.9924	$119.99	$120.00	$120.00
Purchase #3	$119.72	6.828%	$127.8945	$127.89	$127.90	$127.90
Purchase #4	$225.93	11.296%	$251.4511	$251.45	$251.45	$251.50
Purchase #5	$46.90	10.704%	$51.9202	$51.92	$51.90	$51.90
Purchase #6	$247.59	8.841%	$269.4794	$269.48	$269.50	$269.50
Purchase #7	$46.52	13.538%	$52.8179	$52.82	$52.80	$52.80
7 purchase totals =	$861.97		$944.6500	$944.64	$944.65	$944.70