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	$237.37	9.260%	$259.3505	$259.35	$259.35	$259.40
Purchase #2	$173.35	3.179%	$178.8608	$178.86	$178.85	$178.90
Purchase #3	$195.31	3.347%	$201.847	$201.85	$201.85	$201.80
Purchase #4	$204.71	6.798%	$218.6262	$218.63	$218.65	$218.60
Purchase #5	$70.33	3.690%	$72.9252	$72.93	$72.95	$72.90
Purchase #6	$59.71	8.753%	$64.9364	$64.94	$64.95	$64.90
Purchase #7	$6.61	10.856%	$7.3276	$7.33	$7.35	$7.30
7 purchase totals =	$947.39		$1,003.8737	$1,003.89	$1,003.95	$1,003.80