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	$122.70	10.131%	$135.1307	$135.13	$135.15	$135.10
Purchase #2	$109.39	8.150%	$118.3053	$118.31	$118.30	$118.30
Purchase #3	$54.52	8.342%	$59.0681	$59.07	$59.05	$59.10
Purchase #4	$117.31	9.772%	$128.7735	$128.77	$128.75	$128.80
Purchase #5	$213.95	6.152%	$227.1122	$227.11	$227.10	$227.10
Purchase #6	$29.56	6.310%	$31.4252	$31.43	$31.45	$31.40
Purchase #7	$73.34	10.460%	$81.0114	$81.01	$81.00	$81.00
7 purchase totals =	$720.77		$780.8264	$780.83	$780.80	$780.80