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	$39.48	4.211%	$41.1425	$41.14	$41.15	$41.10
Purchase #2	$169.54	9.409%	$185.492	$185.49	$185.50	$185.50
Purchase #3	$197.42	5.574%	$208.4242	$208.42	$208.40	$208.40
Purchase #4	$170.88	11.746%	$190.9516	$190.95	$190.95	$191.00
Purchase #5	$90.55	13.777%	$103.0251	$103.03	$103.05	$103.00
Purchase #6	$89.94	11.618%	$100.3892	$100.39	$100.40	$100.40
Purchase #7	$146.27	9.758%	$160.543	$160.54	$160.55	$160.50
7 purchase totals =	$904.08		$989.9676	$989.96	$990.00	$989.90