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	$220.57	13.109%	$249.4845	$249.48	$249.50	$249.50
Purchase #2	$196.70	7.511%	$211.4741	$211.47	$211.45	$211.50
Purchase #3	$210.69	3.636%	$218.3507	$218.35	$218.35	$218.40
Purchase #4	$6.89	10.127%	$7.5878	$7.59	$7.60	$7.60
Purchase #5	$127.28	3.304%	$131.4853	$131.49	$131.50	$131.50
Purchase #6	$36.79	8.649%	$39.972	$39.97	$39.95	$40.00
Purchase #7	$151.49	6.685%	$161.6171	$161.62	$161.60	$161.60
7 purchase totals =	$950.41		$1,019.9715	$1,019.97	$1,019.95	$1,020.10