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	$80.78	10.360%	$89.1488	$89.15	$89.15	$89.10
Purchase #2	$200.69	9.562%	$219.88	$219.88	$219.90	$219.90
Purchase #3	$57.61	10.826%	$63.8469	$63.85	$63.85	$63.80
Purchase #4	$113.26	4.426%	$118.2729	$118.27	$118.25	$118.30
Purchase #5	$118.59	12.749%	$133.709	$133.71	$133.70	$133.70
Purchase #6	$158.28	8.136%	$171.1577	$171.16	$171.15	$171.20
Purchase #7	$140.54	10.576%	$155.4035	$155.40	$155.40	$155.40
7 purchase totals =	$869.75		$951.4188	$951.42	$951.40	$951.40