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	$237.52	11.529%	$264.9037	$264.90	$264.90	$264.90
Purchase #2	$89.72	9.686%	$98.4103	$98.41	$98.40	$98.40
Purchase #3	$118.32	13.551%	$134.3535	$134.35	$134.35	$134.40
Purchase #4	$175.37	4.645%	$183.5159	$183.52	$183.50	$183.50
Purchase #5	$76.89	7.486%	$82.646	$82.65	$82.65	$82.60
Purchase #6	$152.40	10.594%	$168.5453	$168.55	$168.55	$168.50
Purchase #7	$55.35	6.768%	$59.0961	$59.10	$59.10	$59.10
7 purchase totals =	$905.57		$991.4708	$991.48	$991.45	$991.40