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	$137.25	11.862%	$153.5306	$153.53	$153.55	$153.50
Purchase #2	$35.55	9.199%	$38.8202	$38.82	$38.80	$38.80
Purchase #3	$91.52	7.802%	$98.6604	$98.66	$98.65	$98.70
Purchase #4	$247.55	5.839%	$262.0044	$262.00	$262.00	$262.00
Purchase #5	$145.96	3.225%	$150.6672	$150.67	$150.65	$150.70
Purchase #6	$140.36	8.208%	$151.8807	$151.88	$151.90	$151.90
Purchase #7	$39.95	12.358%	$44.887	$44.89	$44.90	$44.90
7 purchase totals =	$838.14		$900.4505	$900.45	$900.45	$900.50