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	$78.84	13.363%	$89.3754	$89.38	$89.40	$89.40
Purchase #2	$140.76	11.229%	$156.5659	$156.57	$156.55	$156.60
Purchase #3	$198.67	12.759%	$224.0183	$224.02	$224.00	$224.00
Purchase #4	$248.85	5.163%	$261.6981	$261.70	$261.70	$261.70
Purchase #5	$140.82	7.253%	$151.0337	$151.03	$151.05	$151.00
Purchase #6	$231.94	13.812%	$263.9756	$263.98	$264.00	$264.00
Purchase #7	$103.51	13.386%	$117.3658	$117.37	$117.35	$117.40
7 purchase totals =	$1,143.39		$1,264.0328	$1,264.05	$1,264.05	$1,264.10