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	$98.80	4.147%	$102.8972	$102.90	$102.90	$102.90
Purchase #2	$63.70	12.218%	$71.4829	$71.48	$71.50	$71.50
Purchase #3	$131.93	5.283%	$138.8999	$138.90	$138.90	$138.90
Purchase #4	$7.51	11.596%	$8.3809	$8.38	$8.40	$8.40
Purchase #5	$94.34	10.145%	$103.9108	$103.91	$103.90	$103.90
Purchase #6	$90.59	11.210%	$100.7451	$100.75	$100.75	$100.70
Purchase #7	$74.70	11.839%	$83.5437	$83.54	$83.55	$83.50
7 purchase totals =	$561.57		$609.8605	$609.86	$609.90	$609.80