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	$24.30	12.790%	$27.408	$27.41	$27.40	$27.40
Purchase #2	$85.97	5.721%	$90.8883	$90.89	$90.90	$90.90
Purchase #3	$162.29	4.380%	$169.3983	$169.40	$169.40	$169.40
Purchase #4	$62.69	13.398%	$71.0892	$71.09	$71.10	$71.10
Purchase #5	$202.57	10.623%	$224.089	$224.09	$224.10	$224.10
Purchase #6	$58.39	5.575%	$61.6452	$61.65	$61.65	$61.60
Purchase #7	$226.56	13.681%	$257.5557	$257.56	$257.55	$257.60
7 purchase totals =	$822.77		$902.0737	$902.09	$902.10	$902.10