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	$239.70	3.741%	$248.6672	$248.67	$248.65	$248.70
Purchase #2	$213.31	12.836%	$240.6905	$240.69	$240.70	$240.70
Purchase #3	$111.51	6.615%	$118.8864	$118.89	$118.90	$118.90
Purchase #4	$38.34	3.740%	$39.7739	$39.77	$39.75	$39.80
Purchase #5	$62.99	6.208%	$66.9004	$66.90	$66.90	$66.90
Purchase #6	$99.89	9.718%	$109.5973	$109.60	$109.60	$109.60
Purchase #7	$20.63	3.401%	$21.3316	$21.33	$21.35	$21.30
7 purchase totals =	$786.37		$845.8473	$845.85	$845.85	$845.90