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	$235.84	8.805%	$256.6057	$256.61	$256.60	$256.60
Purchase #2	$118.37	10.851%	$131.2143	$131.21	$131.20	$131.20
Purchase #3	$34.69	12.243%	$38.9371	$38.94	$38.95	$38.90
Purchase #4	$38.54	11.200%	$42.8565	$42.86	$42.85	$42.90
Purchase #5	$31.68	3.590%	$32.8173	$32.82	$32.80	$32.80
Purchase #6	$133.41	11.299%	$148.484	$148.48	$148.50	$148.50
Purchase #7	$234.80	13.485%	$266.4628	$266.46	$266.45	$266.50
7 purchase totals =	$827.33		$917.3777	$917.38	$917.35	$917.40