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	$185.35	7.682%	$199.5886	$199.59	$199.60	$199.60
Purchase #2	$68.30	6.342%	$72.6316	$72.63	$72.65	$72.60
Purchase #3	$24.36	10.797%	$26.9901	$26.99	$27.00	$27.00
Purchase #4	$97.97	5.196%	$103.0605	$103.06	$103.05	$103.10
Purchase #5	$33.39	13.566%	$37.9197	$37.92	$37.90	$37.90
Purchase #6	$29.48	10.782%	$32.6585	$32.66	$32.65	$32.70
Purchase #7	$177.92	10.685%	$196.9308	$196.93	$196.95	$196.90
7 purchase totals =	$616.77		$669.7798	$669.78	$669.80	$669.80