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	$33.85	4.598%	$35.4064	$35.41	$35.40	$35.40
Purchase #2	$32.48	4.477%	$33.9341	$33.93	$33.95	$33.90
Purchase #3	$142.57	12.107%	$159.8309	$159.83	$159.85	$159.80
Purchase #4	$39.89	5.104%	$41.926	$41.93	$41.95	$41.90
Purchase #5	$123.82	10.722%	$137.096	$137.10	$137.10	$137.10
Purchase #6	$121.41	8.349%	$131.5465	$131.55	$131.55	$131.50
Purchase #7	$63.81	5.838%	$67.5352	$67.54	$67.55	$67.50
7 purchase totals =	$557.83		$607.2751	$607.29	$607.35	$607.10