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	$83.60	7.424%	$89.8065	$89.81	$89.80	$89.80
Purchase #2	$120.42	13.654%	$136.8621	$136.86	$136.85	$136.90
Purchase #3	$18.92	8.683%	$20.5628	$20.56	$20.55	$20.60
Purchase #4	$98.42	5.252%	$103.589	$103.59	$103.60	$103.60
Purchase #5	$115.34	5.856%	$122.0943	$122.09	$122.10	$122.10
Purchase #6	$37.45	11.861%	$41.8919	$41.89	$41.90	$41.90
Purchase #7	$65.33	10.364%	$72.1008	$72.10	$72.10	$72.10
7 purchase totals =	$539.48		$586.9074	$586.90	$586.90	$587.00