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	$38.29	12.820%	$43.1988	$43.20	$43.20	$43.20
Purchase #2	$185.48	13.481%	$210.4846	$210.48	$210.50	$210.50
Purchase #3	$193.70	11.238%	$215.468	$215.47	$215.45	$215.50
Purchase #4	$14.63	4.600%	$15.303	$15.30	$15.30	$15.30
Purchase #5	$127.48	3.454%	$131.8832	$131.88	$131.90	$131.90
Purchase #6	$38.75	7.493%	$41.6535	$41.65	$41.65	$41.70
Purchase #7	$156.74	10.199%	$172.7259	$172.73	$172.75	$172.70
7 purchase totals =	$755.07		$830.7170	$830.71	$830.75	$830.80