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	$178.65	13.782%	$203.2715	$203.27	$203.25	$203.30
Purchase #2	$150.38	7.372%	$161.466	$161.47	$161.45	$161.50
Purchase #3	$32.97	9.220%	$36.0098	$36.01	$36.00	$36.00
Purchase #4	$153.66	9.322%	$167.9842	$167.98	$168.00	$168.00
Purchase #5	$61.52	6.152%	$65.3047	$65.30	$65.30	$65.30
Purchase #6	$105.37	3.453%	$109.0084	$109.01	$109.00	$109.00
Purchase #7	$52.55	13.153%	$59.4619	$59.46	$59.45	$59.50
7 purchase totals =	$735.10		$802.5065	$802.50	$802.45	$802.60