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	$100.51	11.721%	$112.2908	$112.29	$112.30	$112.30
Purchase #2	$38.49	5.660%	$40.6685	$40.67	$40.65	$40.70
Purchase #3	$35.40	5.308%	$37.279	$37.28	$37.30	$37.30
Purchase #4	$232.90	12.283%	$261.5071	$261.51	$261.50	$261.50
Purchase #5	$198.57	10.507%	$219.4337	$219.43	$219.45	$219.40
Purchase #6	$102.74	13.298%	$116.4024	$116.40	$116.40	$116.40
Purchase #7	$34.51	5.153%	$36.2883	$36.29	$36.30	$36.30
7 purchase totals =	$743.12		$823.8698	$823.87	$823.90	$823.90