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	$48.83	12.183%	$54.779	$54.78	$54.80	$54.80
Purchase #2	$213.47	13.785%	$242.8968	$242.90	$242.90	$242.90
Purchase #3	$233.91	11.313%	$260.3722	$260.37	$260.35	$260.40
Purchase #4	$234.37	11.619%	$261.6015	$261.60	$261.60	$261.60
Purchase #5	$158.56	6.549%	$168.9441	$168.94	$168.95	$168.90
Purchase #6	$95.41	8.269%	$103.2995	$103.30	$103.30	$103.30
Purchase #7	$165.89	13.369%	$188.0678	$188.07	$188.05	$188.10
7 purchase totals =	$1,150.44		$1,279.9609	$1,279.96	$1,279.95	$1,280.00