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	$109.40	3.476%	$113.2027	$113.20	$113.20	$113.20
Purchase #2	$20.39	5.660%	$21.5441	$21.54	$21.55	$21.50
Purchase #3	$169.68	12.218%	$190.4115	$190.41	$190.40	$190.40
Purchase #4	$119.34	12.692%	$134.4866	$134.49	$134.50	$134.50
Purchase #5	$31.61	8.365%	$34.2542	$34.25	$34.25	$34.30
Purchase #6	$27.71	3.352%	$28.6388	$28.64	$28.65	$28.60
Purchase #7	$72.73	13.209%	$82.3369	$82.34	$82.35	$82.30
7 purchase totals =	$550.86		$604.8748	$604.87	$604.90	$604.80