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	$8.56	5.287%	$9.0126	$9.01	$9.00	$9.00
Purchase #2	$215.45	3.522%	$223.0381	$223.04	$223.05	$223.00
Purchase #3	$160.63	9.762%	$176.3107	$176.31	$176.30	$176.30
Purchase #4	$167.35	6.580%	$178.3616	$178.36	$178.35	$178.40
Purchase #5	$76.44	3.170%	$78.8631	$78.86	$78.85	$78.90
Purchase #6	$76.48	13.472%	$86.7834	$86.78	$86.80	$86.80
Purchase #7	$33.56	11.290%	$37.3489	$37.35	$37.35	$37.30
7 purchase totals =	$738.47		$789.7184	$789.71	$789.70	$789.70