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	$47.88	4.581%	$50.0734	$50.07	$50.05	$50.10
Purchase #2	$140.33	4.626%	$146.8217	$146.82	$146.80	$146.80
Purchase #3	$123.93	7.643%	$133.402	$133.40	$133.40	$133.40
Purchase #4	$134.28	5.543%	$141.7231	$141.72	$141.70	$141.70
Purchase #5	$208.39	12.597%	$234.6409	$234.64	$234.65	$234.60
Purchase #6	$205.75	13.417%	$233.3555	$233.36	$233.35	$233.40
Purchase #7	$133.25	10.256%	$146.9161	$146.92	$146.90	$146.90
7 purchase totals =	$993.81		$1,086.9327	$1,086.93	$1,086.85	$1,086.90