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	$148.27	6.211%	$157.479	$157.48	$157.50	$157.50
Purchase #2	$28.30	11.604%	$31.5839	$31.58	$31.60	$31.60
Purchase #3	$51.44	12.457%	$57.8479	$57.85	$57.85	$57.80
Purchase #4	$25.90	13.121%	$29.2983	$29.30	$29.30	$29.30
Purchase #5	$39.32	4.310%	$41.0147	$41.01	$41.00	$41.00
Purchase #6	$177.79	12.839%	$200.6165	$200.62	$200.60	$200.60
Purchase #7	$40.33	8.767%	$43.8657	$43.87	$43.85	$43.90
7 purchase totals =	$511.35		$561.7060	$561.71	$561.70	$561.70