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	$112.69	10.607%	$124.643	$124.64	$124.65	$124.60
Purchase #2	$182.50	8.800%	$198.56	$198.56	$198.55	$198.60
Purchase #3	$99.46	10.538%	$109.9411	$109.94	$109.95	$109.90
Purchase #4	$229.80	5.343%	$242.0782	$242.08	$242.10	$242.10
Purchase #5	$79.91	13.414%	$90.6291	$90.63	$90.65	$90.60
Purchase #6	$110.71	5.309%	$116.5876	$116.59	$116.60	$116.60
Purchase #7	$35.83	4.543%	$37.4578	$37.46	$37.45	$37.50
7 purchase totals =	$850.90		$919.8968	$919.90	$919.95	$919.90