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	$79.44	13.260%	$89.9737	$89.97	$89.95	$90.00
Purchase #2	$203.62	9.590%	$223.1472	$223.15	$223.15	$223.10
Purchase #3	$148.83	13.179%	$168.4443	$168.44	$168.45	$168.40
Purchase #4	$213.56	6.326%	$227.0698	$227.07	$227.05	$227.10
Purchase #5	$214.56	4.785%	$224.8267	$224.83	$224.85	$224.80
Purchase #6	$67.42	6.203%	$71.6021	$71.60	$71.60	$71.60
Purchase #7	$242.44	13.286%	$274.6506	$274.65	$274.65	$274.70
7 purchase totals =	$1,169.87		$1,279.7144	$1,279.71	$1,279.70	$1,279.70