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	$58.73	4.599%	$61.431	$61.43	$61.45	$61.40
Purchase #2	$217.48	5.729%	$229.9394	$229.94	$229.95	$229.90
Purchase #3	$100.99	12.587%	$113.7016	$113.70	$113.70	$113.70
Purchase #4	$109.92	12.551%	$123.7161	$123.72	$123.70	$123.70
Purchase #5	$212.34	8.688%	$230.7881	$230.79	$230.80	$230.80
Purchase #6	$133.39	5.311%	$140.4743	$140.47	$140.45	$140.50
Purchase #7	$91.63	8.150%	$99.0978	$99.10	$99.10	$99.10
7 purchase totals =	$924.48		$999.1483	$999.15	$999.15	$999.10