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	$28.95	13.728%	$32.9243	$32.92	$32.90	$32.90
Purchase #2	$247.29	13.519%	$280.7211	$280.72	$280.70	$280.70
Purchase #3	$216.94	5.815%	$229.5551	$229.56	$229.55	$229.60
Purchase #4	$140.92	11.123%	$156.5945	$156.59	$156.60	$156.60
Purchase #5	$196.65	6.227%	$208.8954	$208.90	$208.90	$208.90
Purchase #6	$216.29	5.864%	$228.9732	$228.97	$228.95	$229.00
Purchase #7	$39.36	12.401%	$44.241	$44.24	$44.25	$44.20
7 purchase totals =	$1,086.40		$1,181.9046	$1,181.90	$1,181.85	$1,181.90