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	$104.83	11.777%	$117.1758	$117.18	$117.20	$117.20
Purchase #2	$71.67	6.356%	$76.2253	$76.23	$76.25	$76.20
Purchase #3	$176.72	11.119%	$196.3695	$196.37	$196.35	$196.40
Purchase #4	$38.87	3.848%	$40.3657	$40.37	$40.35	$40.40
Purchase #5	$211.66	5.617%	$223.5489	$223.55	$223.55	$223.50
Purchase #6	$169.74	7.513%	$182.4926	$182.49	$182.50	$182.50
Purchase #7	$130.79	9.798%	$143.6048	$143.60	$143.60	$143.60
7 purchase totals =	$904.28		$979.7826	$979.79	$979.80	$979.80