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	$220.43	4.292%	$229.8909	$229.89	$229.90	$229.90
Purchase #2	$80.33	12.550%	$90.4114	$90.41	$90.40	$90.40
Purchase #3	$112.28	10.667%	$124.2569	$124.26	$124.25	$124.30
Purchase #4	$182.59	7.565%	$196.4029	$196.40	$196.40	$196.40
Purchase #5	$5.48	11.143%	$6.0906	$6.09	$6.10	$6.10
Purchase #6	$49.25	4.704%	$51.5667	$51.57	$51.55	$51.60
Purchase #7	$9.98	8.191%	$10.7975	$10.80	$10.80	$10.80
7 purchase totals =	$660.34		$709.4169	$709.42	$709.40	$709.50