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	$134.78	10.180%	$148.5006	$148.50	$148.50	$148.50
Purchase #2	$65.87	8.330%	$71.357	$71.36	$71.35	$71.40
Purchase #3	$114.38	3.652%	$118.5572	$118.56	$118.55	$118.60
Purchase #4	$65.30	11.284%	$72.6685	$72.67	$72.65	$72.70
Purchase #5	$82.43	12.678%	$92.8805	$92.88	$92.90	$92.90
Purchase #6	$43.64	4.664%	$45.6754	$45.68	$45.70	$45.70
Purchase #7	$156.33	4.657%	$163.6103	$163.61	$163.60	$163.60
7 purchase totals =	$662.73		$713.2495	$713.26	$713.25	$713.40