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	$48.87	6.596%	$52.0935	$52.09	$52.10	$52.10
Purchase #2	$45.64	7.274%	$48.9599	$48.96	$48.95	$49.00
Purchase #3	$91.56	12.107%	$102.6452	$102.65	$102.65	$102.60
Purchase #4	$205.50	9.420%	$224.8581	$224.86	$224.85	$224.90
Purchase #5	$79.83	13.191%	$90.3604	$90.36	$90.35	$90.40
Purchase #6	$180.80	8.762%	$196.6417	$196.64	$196.65	$196.60
Purchase #7	$208.86	4.534%	$218.3297	$218.33	$218.35	$218.30
7 purchase totals =	$861.06		$933.8885	$933.89	$933.90	$933.90