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	$35.42	9.783%	$38.8851	$38.89	$38.90	$38.90
Purchase #2	$160.39	13.700%	$182.3634	$182.36	$182.35	$182.40
Purchase #3	$128.58	6.823%	$137.353	$137.35	$137.35	$137.40
Purchase #4	$75.32	4.263%	$78.5309	$78.53	$78.55	$78.50
Purchase #5	$196.82	10.466%	$217.4192	$217.42	$217.40	$217.40
Purchase #6	$70.64	3.395%	$73.0382	$73.04	$73.05	$73.00
Purchase #7	$79.55	3.219%	$82.1107	$82.11	$82.10	$82.10
7 purchase totals =	$746.72		$809.7005	$809.70	$809.70	$809.70