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	$77.77	5.759%	$82.2488	$82.25	$82.25	$82.20
Purchase #2	$121.81	12.317%	$136.8133	$136.81	$136.80	$136.80
Purchase #3	$151.65	7.383%	$162.8463	$162.85	$162.85	$162.80
Purchase #4	$201.78	12.155%	$226.3064	$226.31	$226.30	$226.30
Purchase #5	$93.38	11.246%	$103.8815	$103.88	$103.90	$103.90
Purchase #6	$103.51	4.594%	$108.2652	$108.27	$108.25	$108.30
Purchase #7	$226.69	7.241%	$243.1046	$243.10	$243.10	$243.10
7 purchase totals =	$976.59		$1,063.4661	$1,063.47	$1,063.45	$1,063.40