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	$83.58	7.162%	$89.566	$89.57	$89.55	$89.60
Purchase #2	$30.31	6.857%	$32.3884	$32.39	$32.40	$32.40
Purchase #3	$193.31	13.212%	$218.8501	$218.85	$218.85	$218.90
Purchase #4	$28.93	9.628%	$31.7154	$31.72	$31.70	$31.70
Purchase #5	$200.67	9.208%	$219.1477	$219.15	$219.15	$219.10
Purchase #6	$170.84	4.404%	$178.3638	$178.36	$178.35	$178.40
Purchase #7	$169.92	12.240%	$190.7182	$190.72	$190.70	$190.70
7 purchase totals =	$877.56		$960.7496	$960.76	$960.70	$960.80