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	$42.34	6.523%	$45.1018	$45.10	$45.10	$45.10
Purchase #2	$201.44	6.628%	$214.7914	$214.79	$214.80	$214.80
Purchase #3	$80.38	11.545%	$89.6599	$89.66	$89.65	$89.70
Purchase #4	$239.93	10.785%	$265.8065	$265.81	$265.80	$265.80
Purchase #5	$37.93	3.164%	$39.1301	$39.13	$39.15	$39.10
Purchase #6	$198.33	13.390%	$224.8864	$224.89	$224.90	$224.90
Purchase #7	$40.87	7.675%	$44.0068	$44.01	$44.00	$44.00
7 purchase totals =	$841.22		$923.3829	$923.39	$923.40	$923.40