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	$92.67	3.826%	$96.2156	$96.22	$96.20	$96.20
Purchase #2	$175.48	13.154%	$198.5626	$198.56	$198.55	$198.60
Purchase #3	$91.38	8.620%	$99.257	$99.26	$99.25	$99.30
Purchase #4	$206.66	7.869%	$222.9221	$222.92	$222.90	$222.90
Purchase #5	$54.57	13.729%	$62.0619	$62.06	$62.05	$62.10
Purchase #6	$241.41	5.651%	$255.0521	$255.05	$255.05	$255.10
Purchase #7	$43.50	5.619%	$45.9443	$45.94	$45.95	$45.90
7 purchase totals =	$905.67		$980.0156	$980.01	$979.95	$980.10