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	$231.88	3.621%	$240.2764	$240.28	$240.30	$240.30
Purchase #2	$205.77	12.566%	$231.6271	$231.63	$231.65	$231.60
Purchase #3	$51.50	12.267%	$57.8175	$57.82	$57.80	$57.80
Purchase #4	$71.57	9.602%	$78.4422	$78.44	$78.45	$78.40
Purchase #5	$72.32	11.241%	$80.4495	$80.45	$80.45	$80.40
Purchase #6	$245.51	12.858%	$277.0777	$277.08	$277.10	$277.10
Purchase #7	$25.75	8.260%	$27.877	$27.88	$27.90	$27.90
7 purchase totals =	$904.30		$993.5674	$993.58	$993.65	$993.50