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	$35.75	11.422%	$39.8334	$39.83	$39.85	$39.80
Purchase #2	$37.63	13.377%	$42.6638	$42.66	$42.65	$42.70
Purchase #3	$33.70	8.185%	$36.4583	$36.46	$36.45	$36.50
Purchase #4	$123.94	8.798%	$134.8442	$134.84	$134.85	$134.80
Purchase #5	$178.40	10.391%	$196.9375	$196.94	$196.95	$196.90
Purchase #6	$87.62	11.719%	$97.8882	$97.89	$97.90	$97.90
Purchase #7	$110.47	7.519%	$118.7762	$118.78	$118.80	$118.80
7 purchase totals =	$607.51		$667.4016	$667.40	$667.45	$667.40