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	$43.46	12.709%	$48.9833	$48.98	$49.00	$49.00
Purchase #2	$51.57	4.821%	$54.0562	$54.06	$54.05	$54.10
Purchase #3	$168.82	13.162%	$191.0401	$191.04	$191.05	$191.00
Purchase #4	$58.48	6.207%	$62.1099	$62.11	$62.10	$62.10
Purchase #5	$140.47	9.410%	$153.6882	$153.69	$153.70	$153.70
Purchase #6	$6.31	9.146%	$6.8871	$6.89	$6.90	$6.90
Purchase #7	$164.72	12.339%	$185.0448	$185.04	$185.05	$185.00
7 purchase totals =	$633.83		$701.8096	$701.81	$701.85	$701.80