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	$79.65	4.814%	$83.4844	$83.48	$83.50	$83.50
Purchase #2	$172.46	8.651%	$187.3795	$187.38	$187.40	$187.40
Purchase #3	$84.94	5.287%	$89.4308	$89.43	$89.45	$89.40
Purchase #4	$17.65	9.738%	$19.3688	$19.37	$19.35	$19.40
Purchase #5	$129.50	7.826%	$139.6347	$139.63	$139.65	$139.60
Purchase #6	$150.54	3.614%	$155.9805	$155.98	$156.00	$156.00
Purchase #7	$96.56	6.639%	$102.9706	$102.97	$102.95	$103.00
7 purchase totals =	$731.30		$778.2493	$778.24	$778.30	$778.30