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	$162.87	10.453%	$179.8948	$179.89	$179.90	$179.90
Purchase #2	$37.76	6.724%	$40.299	$40.30	$40.30	$40.30
Purchase #3	$172.88	3.371%	$178.7078	$178.71	$178.70	$178.70
Purchase #4	$127.50	9.811%	$140.009	$140.01	$140.00	$140.00
Purchase #5	$136.66	12.463%	$153.6919	$153.69	$153.70	$153.70
Purchase #6	$40.35	3.253%	$41.6626	$41.66	$41.65	$41.70
Purchase #7	$220.48	10.225%	$243.0241	$243.02	$243.00	$243.00
7 purchase totals =	$898.50		$977.2892	$977.28	$977.25	$977.30