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	$138.35	10.650%	$153.0843	$153.08	$153.10	$153.10
Purchase #2	$155.27	8.508%	$168.4804	$168.48	$168.50	$168.50
Purchase #3	$178.39	11.259%	$198.4749	$198.47	$198.45	$198.50
Purchase #4	$92.96	12.736%	$104.7994	$104.80	$104.80	$104.80
Purchase #5	$144.75	6.815%	$154.6147	$154.61	$154.60	$154.60
Purchase #6	$28.78	4.666%	$30.1229	$30.12	$30.10	$30.10
Purchase #7	$38.28	11.605%	$42.7224	$42.72	$42.70	$42.70
7 purchase totals =	$776.78		$852.2990	$852.28	$852.25	$852.30