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	$140.48	6.394%	$149.4623	$149.46	$149.45	$149.50
Purchase #2	$48.91	10.370%	$53.982	$53.98	$54.00	$54.00
Purchase #3	$37.39	12.564%	$42.0877	$42.09	$42.10	$42.10
Purchase #4	$115.47	7.187%	$123.7688	$123.77	$123.75	$123.80
Purchase #5	$10.93	6.538%	$11.6446	$11.64	$11.65	$11.60
Purchase #6	$225.86	11.527%	$251.8949	$251.89	$251.90	$251.90
Purchase #7	$177.50	6.745%	$189.4724	$189.47	$189.45	$189.50
7 purchase totals =	$756.54		$822.3127	$822.30	$822.30	$822.40