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	$103.54	4.547%	$108.248	$108.25	$108.25	$108.20
Purchase #2	$119.57	9.580%	$131.0248	$131.02	$131.00	$131.00
Purchase #3	$37.31	5.220%	$39.2576	$39.26	$39.25	$39.30
Purchase #4	$245.64	6.371%	$261.2897	$261.29	$261.30	$261.30
Purchase #5	$109.45	12.842%	$123.5056	$123.51	$123.50	$123.50
Purchase #6	$97.56	6.439%	$103.8419	$103.84	$103.85	$103.80
Purchase #7	$29.48	13.233%	$33.3811	$33.38	$33.40	$33.40
7 purchase totals =	$742.55		$800.5487	$800.55	$800.55	$800.50