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	$115.84	10.360%	$127.841	$127.84	$127.85	$127.80
Purchase #2	$128.61	9.277%	$140.5411	$140.54	$140.55	$140.50
Purchase #3	$101.75	12.752%	$114.7252	$114.73	$114.75	$114.70
Purchase #4	$7.90	12.237%	$8.8667	$8.87	$8.85	$8.90
Purchase #5	$77.48	7.776%	$83.5048	$83.50	$83.50	$83.50
Purchase #6	$154.56	8.419%	$167.5724	$167.57	$167.55	$167.60
Purchase #7	$36.89	13.246%	$41.7764	$41.78	$41.80	$41.80
7 purchase totals =	$623.03		$684.8276	$684.83	$684.85	$684.80