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	3.772%	$103.2635	$103.26	$103.25	$103.30
Purchase #2	$210.71	7.107%	$225.6852	$225.69	$225.70	$225.70
Purchase #3	$140.32	5.497%	$148.0334	$148.03	$148.05	$148.00
Purchase #4	$81.25	12.348%	$91.2828	$91.28	$91.30	$91.30
Purchase #5	$47.87	8.394%	$51.8882	$51.89	$51.90	$51.90
Purchase #6	$82.51	10.530%	$91.1983	$91.20	$91.20	$91.20
Purchase #7	$38.39	10.492%	$42.4179	$42.42	$42.40	$42.40
7 purchase totals =	$700.56		$753.7693	$753.77	$753.80	$753.80