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	$8.57	5.781%	$9.0654	$9.07	$9.05	$9.10
Purchase #2	$239.48	4.211%	$249.5645	$249.56	$249.55	$249.60
Purchase #3	$126.30	4.834%	$132.4053	$132.41	$132.40	$132.40
Purchase #4	$52.25	6.254%	$55.5177	$55.52	$55.50	$55.50
Purchase #5	$48.62	13.381%	$55.1258	$55.13	$55.15	$55.10
Purchase #6	$67.87	4.832%	$71.1495	$71.15	$71.15	$71.10
Purchase #7	$56.44	5.772%	$59.6977	$59.70	$59.70	$59.70
7 purchase totals =	$599.53		$632.5259	$632.54	$632.50	$632.50