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	$118.30	8.820%	$128.7341	$128.73	$128.75	$128.70
Purchase #2	$162.69	4.410%	$169.8646	$169.86	$169.85	$169.90
Purchase #3	$210.74	13.814%	$239.8516	$239.85	$239.85	$239.90
Purchase #4	$93.25	12.827%	$105.2112	$105.21	$105.20	$105.20
Purchase #5	$84.74	7.259%	$90.8913	$90.89	$90.90	$90.90
Purchase #6	$79.58	10.408%	$87.8627	$87.86	$87.85	$87.90
Purchase #7	$9.47	12.379%	$10.6423	$10.64	$10.65	$10.60
7 purchase totals =	$758.77		$833.0578	$833.04	$833.05	$833.10