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	$129.70	10.652%	$143.5156	$143.52	$143.50	$143.50
Purchase #2	$7.60	6.372%	$8.0843	$8.08	$8.10	$8.10
Purchase #3	$231.75	10.405%	$255.8636	$255.86	$255.85	$255.90
Purchase #4	$179.32	3.782%	$186.1019	$186.10	$186.10	$186.10
Purchase #5	$79.89	12.165%	$89.6086	$89.61	$89.60	$89.60
Purchase #6	$140.92	5.443%	$148.5903	$148.59	$148.60	$148.60
Purchase #7	$221.89	5.490%	$234.0718	$234.07	$234.05	$234.10
7 purchase totals =	$991.07		$1,065.8361	$1,065.83	$1,065.80	$1,065.90