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	$60.92	8.735%	$66.2414	$66.24	$66.25	$66.20
Purchase #2	$99.72	4.675%	$104.3819	$104.38	$104.40	$104.40
Purchase #3	$203.38	12.656%	$229.1198	$229.12	$229.10	$229.10
Purchase #4	$248.79	9.643%	$272.7808	$272.78	$272.80	$272.80
Purchase #5	$87.88	3.447%	$90.9092	$90.91	$90.90	$90.90
Purchase #6	$39.32	10.150%	$43.311	$43.31	$43.30	$43.30
Purchase #7	$49.86	3.430%	$51.5702	$51.57	$51.55	$51.60
7 purchase totals =	$789.87		$858.3143	$858.31	$858.30	$858.30