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	$52.89	5.671%	$55.8894	$55.89	$55.90	$55.90
Purchase #2	$188.73	13.115%	$213.4819	$213.48	$213.50	$213.50
Purchase #3	$211.40	12.196%	$237.1823	$237.18	$237.20	$237.20
Purchase #4	$37.74	12.712%	$42.5375	$42.54	$42.55	$42.50
Purchase #5	$64.40	10.725%	$71.3069	$71.31	$71.30	$71.30
Purchase #6	$87.63	12.287%	$98.3971	$98.40	$98.40	$98.40
Purchase #7	$175.93	13.766%	$200.1485	$200.15	$200.15	$200.10
7 purchase totals =	$818.72		$918.9436	$918.95	$919.00	$918.90