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	$153.62	11.838%	$171.8055	$171.81	$171.80	$171.80
Purchase #2	$188.67	6.149%	$200.2713	$200.27	$200.25	$200.30
Purchase #3	$46.63	9.601%	$51.1069	$51.11	$51.10	$51.10
Purchase #4	$232.27	9.852%	$255.1532	$255.15	$255.15	$255.20
Purchase #5	$67.96	6.580%	$72.4318	$72.43	$72.45	$72.40
Purchase #6	$61.62	12.252%	$69.1697	$69.17	$69.15	$69.20
Purchase #7	$93.29	7.299%	$100.0992	$100.10	$100.10	$100.10
7 purchase totals =	$844.06		$920.0376	$920.04	$920.00	$920.10