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	$246.51	12.804%	$278.0731	$278.07	$278.05	$278.10
Purchase #2	$212.53	11.753%	$237.5087	$237.51	$237.50	$237.50
Purchase #3	$18.74	9.704%	$20.5585	$20.56	$20.55	$20.60
Purchase #4	$172.87	13.744%	$196.6293	$196.63	$196.65	$196.60
Purchase #5	$108.37	7.652%	$116.6625	$116.66	$116.65	$116.70
Purchase #6	$44.32	10.280%	$48.8761	$48.88	$48.90	$48.90
Purchase #7	$90.32	10.817%	$100.0899	$100.09	$100.10	$100.10
7 purchase totals =	$893.66		$998.3981	$998.40	$998.40	$998.50