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	$99.51	9.857%	$109.3187	$109.32	$109.30	$109.30
Purchase #2	$91.52	3.494%	$94.7177	$94.72	$94.70	$94.70
Purchase #3	$75.86	7.692%	$81.6952	$81.70	$81.70	$81.70
Purchase #4	$199.48	11.746%	$222.9109	$222.91	$222.90	$222.90
Purchase #5	$124.56	11.813%	$139.2743	$139.27	$139.25	$139.30
Purchase #6	$75.59	9.732%	$82.9464	$82.95	$82.95	$82.90
Purchase #7	$46.31	7.582%	$49.8212	$49.82	$49.80	$49.80
7 purchase totals =	$712.83		$780.6844	$780.69	$780.60	$780.60