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	$23.25	12.522%	$26.1614	$26.16	$26.15	$26.20
Purchase #2	$141.44	6.664%	$150.8656	$150.87	$150.85	$150.90
Purchase #3	$121.84	4.855%	$127.7553	$127.76	$127.75	$127.80
Purchase #4	$242.45	9.233%	$264.8354	$264.84	$264.85	$264.80
Purchase #5	$108.31	5.121%	$113.8566	$113.86	$113.85	$113.90
Purchase #6	$248.88	6.417%	$264.8506	$264.85	$264.85	$264.90
Purchase #7	$123.54	10.550%	$136.5735	$136.57	$136.55	$136.60
7 purchase totals =	$1,009.71		$1,084.8984	$1,084.91	$1,084.85	$1,085.10