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	$37.28	4.321%	$38.8909	$38.89	$38.90	$38.90
Purchase #2	$175.66	4.783%	$184.0618	$184.06	$184.05	$184.10
Purchase #3	$58.27	8.172%	$63.0318	$63.03	$63.05	$63.00
Purchase #4	$119.64	3.508%	$123.837	$123.84	$123.85	$123.80
Purchase #5	$31.43	7.286%	$33.72	$33.72	$33.70	$33.70
Purchase #6	$155.76	5.775%	$164.7551	$164.76	$164.75	$164.80
Purchase #7	$152.39	12.691%	$171.7298	$171.73	$171.75	$171.70
7 purchase totals =	$730.43		$780.0264	$780.03	$780.05	$780.00