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	$78.48	5.631%	$82.8992	$82.90	$82.90	$82.90
Purchase #2	$151.81	13.779%	$172.7279	$172.73	$172.75	$172.70
Purchase #3	$129.34	10.532%	$142.9621	$142.96	$142.95	$143.00
Purchase #4	$178.58	11.240%	$198.6524	$198.65	$198.65	$198.70
Purchase #5	$171.59	12.692%	$193.3682	$193.37	$193.35	$193.40
Purchase #6	$99.79	3.591%	$103.3735	$103.37	$103.35	$103.40
Purchase #7	$19.30	3.540%	$19.9832	$19.98	$20.00	$20.00
7 purchase totals =	$828.89		$913.9665	$913.96	$913.95	$914.10