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	$91.52	9.231%	$99.9682	$99.97	$99.95	$100.00
Purchase #2	$165.29	11.225%	$183.8438	$183.84	$183.85	$183.80
Purchase #3	$79.88	7.691%	$86.0236	$86.02	$86.00	$86.00
Purchase #4	$126.45	13.293%	$143.259	$143.26	$143.25	$143.30
Purchase #5	$101.46	12.646%	$114.2906	$114.29	$114.30	$114.30
Purchase #6	$100.53	11.497%	$112.0879	$112.09	$112.10	$112.10
Purchase #7	$82.78	8.179%	$89.5506	$89.55	$89.55	$89.60
7 purchase totals =	$747.91		$829.0237	$829.02	$829.00	$829.10