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	$17.79	13.816%	$20.2479	$20.25	$20.25	$20.20
Purchase #2	$128.37	10.710%	$142.1184	$142.12	$142.10	$142.10
Purchase #3	$132.57	11.479%	$147.7877	$147.79	$147.80	$147.80
Purchase #4	$7.61	4.379%	$7.9432	$7.94	$7.95	$7.90
Purchase #5	$217.58	4.730%	$227.8715	$227.87	$227.85	$227.90
Purchase #6	$27.46	13.193%	$31.0828	$31.08	$31.10	$31.10
Purchase #7	$44.48	5.411%	$46.8868	$46.89	$46.90	$46.90
7 purchase totals =	$575.86		$623.9383	$623.94	$623.95	$623.90