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	$238.30	11.186%	$264.9562	$264.96	$264.95	$265.00
Purchase #2	$98.57	7.427%	$105.8908	$105.89	$105.90	$105.90
Purchase #3	$208.37	6.678%	$222.2849	$222.28	$222.30	$222.30
Purchase #4	$70.52	10.672%	$78.0459	$78.05	$78.05	$78.00
Purchase #5	$153.66	10.466%	$169.7421	$169.74	$169.75	$169.70
Purchase #6	$162.98	12.214%	$182.8864	$182.89	$182.90	$182.90
Purchase #7	$240.51	6.496%	$256.1335	$256.13	$256.15	$256.10
7 purchase totals =	$1,172.91		$1,279.9398	$1,279.94	$1,280.00	$1,279.90