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	$157.83	13.497%	$179.1323	$179.13	$179.15	$179.10
Purchase #2	$31.39	6.266%	$33.3569	$33.36	$33.35	$33.40
Purchase #3	$141.78	10.725%	$156.9859	$156.99	$157.00	$157.00
Purchase #4	$57.87	5.417%	$61.0048	$61.00	$61.00	$61.00
Purchase #5	$89.86	6.478%	$95.6811	$95.68	$95.70	$95.70
Purchase #6	$51.78	11.317%	$57.6399	$57.64	$57.65	$57.60
Purchase #7	$192.25	12.175%	$215.6564	$215.66	$215.65	$215.70
7 purchase totals =	$722.76		$799.4573	$799.46	$799.50	$799.50