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	$123.78	7.764%	$133.3903	$133.39	$133.40	$133.40
Purchase #2	$43.71	10.693%	$48.3839	$48.38	$48.40	$48.40
Purchase #3	$31.37	7.506%	$33.7246	$33.72	$33.70	$33.70
Purchase #4	$61.94	11.776%	$69.2341	$69.23	$69.25	$69.20
Purchase #5	$246.59	13.692%	$280.3531	$280.35	$280.35	$280.40
Purchase #6	$176.43	6.826%	$188.4731	$188.47	$188.45	$188.50
Purchase #7	$137.39	8.384%	$148.9088	$148.91	$148.90	$148.90
7 purchase totals =	$821.21		$902.4679	$902.45	$902.45	$902.50