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	$142.59	12.580%	$160.5278	$160.53	$160.55	$160.50
Purchase #2	$45.46	10.641%	$50.2974	$50.30	$50.30	$50.30
Purchase #3	$228.78	12.849%	$258.1759	$258.18	$258.20	$258.20
Purchase #4	$73.82	11.438%	$82.2635	$82.26	$82.25	$82.30
Purchase #5	$177.93	6.626%	$189.7196	$189.72	$189.70	$189.70
Purchase #6	$104.94	7.568%	$112.8819	$112.88	$112.90	$112.90
Purchase #7	$207.87	12.331%	$233.5024	$233.50	$233.50	$233.50
7 purchase totals =	$981.39		$1,087.3685	$1,087.37	$1,087.40	$1,087.40