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	$6.93	4.442%	$7.2378	$7.24	$7.25	$7.20
Purchase #2	$249.72	5.141%	$262.5581	$262.56	$262.55	$262.60
Purchase #3	$50.27	3.258%	$51.9078	$51.91	$51.90	$51.90
Purchase #4	$19.45	7.116%	$20.8341	$20.83	$20.85	$20.80
Purchase #5	$25.96	9.708%	$28.4802	$28.48	$28.50	$28.50
Purchase #6	$131.58	10.761%	$145.7393	$145.74	$145.75	$145.70
Purchase #7	$117.48	7.333%	$126.0948	$126.09	$126.10	$126.10
7 purchase totals =	$601.39		$642.8521	$642.85	$642.90	$642.80