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	$78.45	6.168%	$83.2888	$83.29	$83.30	$83.30
Purchase #2	$156.33	9.515%	$171.2048	$171.20	$171.20	$171.20
Purchase #3	$20.98	9.737%	$23.0228	$23.02	$23.00	$23.00
Purchase #4	$137.30	3.281%	$141.8048	$141.80	$141.80	$141.80
Purchase #5	$133.44	8.528%	$144.8198	$144.82	$144.80	$144.80
Purchase #6	$158.83	12.685%	$178.9776	$178.98	$179.00	$179.00
Purchase #7	$128.27	3.280%	$132.4773	$132.48	$132.50	$132.50
7 purchase totals =	$813.60		$875.5959	$875.59	$875.60	$875.60