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	$11.99	3.802%	$12.4459	$12.45	$12.45	$12.40
Purchase #2	$235.86	4.582%	$246.6671	$246.67	$246.65	$246.70
Purchase #3	$85.67	5.841%	$90.674	$90.67	$90.65	$90.70
Purchase #4	$204.52	4.397%	$213.5127	$213.51	$213.50	$213.50
Purchase #5	$38.61	7.718%	$41.5899	$41.59	$41.60	$41.60
Purchase #6	$147.47	11.819%	$164.8995	$164.90	$164.90	$164.90
Purchase #7	$200.54	9.566%	$219.7237	$219.72	$219.70	$219.70
7 purchase totals =	$924.66		$989.5128	$989.51	$989.45	$989.50