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	$164.99	3.813%	$171.2811	$171.28	$171.30	$171.30
Purchase #2	$223.86	6.323%	$238.0147	$238.01	$238.00	$238.00
Purchase #3	$29.30	8.676%	$31.8421	$31.84	$31.85	$31.80
Purchase #4	$26.27	4.224%	$27.3796	$27.38	$27.40	$27.40
Purchase #5	$136.64	11.713%	$152.6446	$152.64	$152.65	$152.60
Purchase #6	$35.44	8.462%	$38.4389	$38.44	$38.45	$38.40
Purchase #7	$103.27	5.673%	$109.1285	$109.13	$109.15	$109.10
7 purchase totals =	$719.77		$768.7295	$768.72	$768.80	$768.60