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	$129.67	12.840%	$146.3196	$146.32	$146.30	$146.30
Purchase #2	$80.40	4.239%	$83.8082	$83.81	$83.80	$83.80
Purchase #3	$115.61	6.704%	$123.3605	$123.36	$123.35	$123.40
Purchase #4	$83.93	11.820%	$93.8505	$93.85	$93.85	$93.90
Purchase #5	$97.88	13.410%	$111.0057	$111.01	$111.00	$111.00
Purchase #6	$206.60	10.675%	$228.6546	$228.65	$228.65	$228.70
Purchase #7	$31.58	13.535%	$35.8544	$35.85	$35.85	$35.90
7 purchase totals =	$745.67		$822.8535	$822.85	$822.80	$823.00