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	$134.25	6.759%	$143.324	$143.32	$143.30	$143.30
Purchase #2	$30.71	11.646%	$34.2865	$34.29	$34.30	$34.30
Purchase #3	$40.59	6.238%	$43.122	$43.12	$43.10	$43.10
Purchase #4	$82.78	5.495%	$87.3288	$87.33	$87.35	$87.30
Purchase #5	$56.45	13.813%	$64.2474	$64.25	$64.25	$64.20
Purchase #6	$248.49	12.769%	$280.2197	$280.22	$280.20	$280.20
Purchase #7	$196.32	3.571%	$203.3306	$203.33	$203.35	$203.30
7 purchase totals =	$789.59		$855.8590	$855.86	$855.85	$855.70