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	$29.48	9.123%	$32.1695	$32.17	$32.15	$32.20
Purchase #2	$122.89	11.243%	$136.7065	$136.71	$136.70	$136.70
Purchase #3	$58.27	12.425%	$65.51	$65.51	$65.50	$65.50
Purchase #4	$196.62	6.190%	$208.7908	$208.79	$208.80	$208.80
Purchase #5	$234.46	5.273%	$246.8231	$246.82	$246.80	$246.80
Purchase #6	$244.85	9.403%	$267.8732	$267.87	$267.85	$267.90
Purchase #7	$49.88	6.168%	$52.9566	$52.96	$52.95	$53.00
7 purchase totals =	$936.45		$1,010.8297	$1,010.83	$1,010.75	$1,010.90