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	$34.43	12.131%	$38.6067	$38.61	$38.60	$38.60
Purchase #2	$196.46	10.695%	$217.4714	$217.47	$217.45	$217.50
Purchase #3	$37.41	3.150%	$38.5884	$38.59	$38.60	$38.60
Purchase #4	$221.39	3.127%	$228.3129	$228.31	$228.30	$228.30
Purchase #5	$199.31	10.340%	$219.9187	$219.92	$219.90	$219.90
Purchase #6	$123.49	4.717%	$129.315	$129.32	$129.30	$129.30
Purchase #7	$92.35	3.597%	$95.6718	$95.67	$95.65	$95.70
7 purchase totals =	$904.84		$967.8849	$967.89	$967.80	$967.90