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	$14.62	3.606%	$15.1472	$15.15	$15.15	$15.10
Purchase #2	$208.90	12.281%	$234.555	$234.56	$234.55	$234.60
Purchase #3	$165.49	6.286%	$175.8927	$175.89	$175.90	$175.90
Purchase #4	$153.86	9.265%	$168.1151	$168.12	$168.10	$168.10
Purchase #5	$20.69	5.859%	$21.9022	$21.90	$21.90	$21.90
Purchase #6	$158.34	8.490%	$171.7831	$171.78	$171.80	$171.80
Purchase #7	$67.56	7.380%	$72.5459	$72.55	$72.55	$72.50
7 purchase totals =	$789.46		$859.9412	$859.95	$859.95	$859.90