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	$173.29	7.810%	$186.8239	$186.82	$186.80	$186.80
Purchase #2	$87.33	3.241%	$90.1604	$90.16	$90.15	$90.20
Purchase #3	$215.33	10.127%	$237.1365	$237.14	$237.15	$237.10
Purchase #4	$40.32	8.753%	$43.8492	$43.85	$43.85	$43.80
Purchase #5	$113.83	8.234%	$123.2028	$123.20	$123.20	$123.20
Purchase #6	$159.54	9.653%	$174.9404	$174.94	$174.95	$174.90
Purchase #7	$151.61	6.416%	$161.3373	$161.34	$161.35	$161.30
7 purchase totals =	$941.25		$1,017.4505	$1,017.45	$1,017.45	$1,017.30