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	$150.58	4.150%	$156.8291	$156.83	$156.85	$156.80
Purchase #2	$43.48	6.241%	$46.1936	$46.19	$46.20	$46.20
Purchase #3	$105.62	12.701%	$119.0348	$119.03	$119.05	$119.00
Purchase #4	$235.90	4.871%	$247.3907	$247.39	$247.40	$247.40
Purchase #5	$57.55	9.346%	$62.9286	$62.93	$62.95	$62.90
Purchase #6	$187.99	4.279%	$196.0341	$196.03	$196.05	$196.00
Purchase #7	$68.68	4.714%	$71.9176	$71.92	$71.90	$71.90
7 purchase totals =	$849.80		$900.3285	$900.32	$900.40	$900.20