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	$246.58	13.222%	$279.1828	$279.18	$279.20	$279.20
Purchase #2	$112.50	10.791%	$124.6399	$124.64	$124.65	$124.60
Purchase #3	$243.83	12.572%	$274.4843	$274.48	$274.50	$274.50
Purchase #4	$186.29	12.113%	$208.8553	$208.86	$208.85	$208.90
Purchase #5	$136.91	4.480%	$143.0436	$143.04	$143.05	$143.00
Purchase #6	$179.28	10.805%	$198.6512	$198.65	$198.65	$198.70
Purchase #7	$82.94	8.254%	$89.7859	$89.79	$89.80	$89.80
7 purchase totals =	$1,188.33		$1,318.6430	$1,318.64	$1,318.70	$1,318.70