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	$199.39	11.677%	$222.6728	$222.67	$222.65	$222.70
Purchase #2	$78.78	5.810%	$83.3571	$83.36	$83.35	$83.40
Purchase #3	$160.39	13.652%	$182.2864	$182.29	$182.30	$182.30
Purchase #4	$239.95	7.150%	$257.1064	$257.11	$257.10	$257.10
Purchase #5	$68.25	4.358%	$71.2243	$71.22	$71.20	$71.20
Purchase #6	$140.94	13.748%	$160.3164	$160.32	$160.30	$160.30
Purchase #7	$29.70	7.390%	$31.8948	$31.89	$31.90	$31.90
7 purchase totals =	$917.40		$1,008.8582	$1,008.86	$1,008.80	$1,008.90