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	$157.97	13.715%	$179.6356	$179.64	$179.65	$179.60
Purchase #2	$232.99	9.675%	$255.5318	$255.53	$255.55	$255.50
Purchase #3	$190.50	11.840%	$213.0552	$213.06	$213.05	$213.10
Purchase #4	$153.44	12.212%	$172.1781	$172.18	$172.20	$172.20
Purchase #5	$194.58	13.835%	$221.5001	$221.50	$221.50	$221.50
Purchase #6	$172.60	10.591%	$190.8801	$190.88	$190.90	$190.90
Purchase #7	$40.92	11.665%	$45.6933	$45.69	$45.70	$45.70
7 purchase totals =	$1,143.00		$1,278.4742	$1,278.48	$1,278.55	$1,278.50