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	$24.52	4.232%	$25.5577	$25.56	$25.55	$25.60
Purchase #2	$196.68	9.498%	$215.3607	$215.36	$215.35	$215.40
Purchase #3	$84.41	3.778%	$87.599	$87.60	$87.60	$87.60
Purchase #4	$117.90	4.458%	$123.156	$123.16	$123.15	$123.20
Purchase #5	$61.57	6.166%	$65.3664	$65.37	$65.35	$65.40
Purchase #6	$237.86	4.256%	$247.9833	$247.98	$248.00	$248.00
Purchase #7	$71.32	10.146%	$78.5561	$78.56	$78.55	$78.60
7 purchase totals =	$794.26		$843.5792	$843.59	$843.55	$843.80