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	$127.53	9.332%	$139.4311	$139.43	$139.45	$139.40
Purchase #2	$40.35	6.854%	$43.1156	$43.12	$43.10	$43.10
Purchase #3	$205.53	3.102%	$211.9055	$211.91	$211.90	$211.90
Purchase #4	$59.57	3.538%	$61.6776	$61.68	$61.70	$61.70
Purchase #5	$124.56	13.827%	$141.7829	$141.78	$141.80	$141.80
Purchase #6	$128.85	12.219%	$144.5942	$144.59	$144.60	$144.60
Purchase #7	$246.52	11.427%	$274.6898	$274.69	$274.70	$274.70
7 purchase totals =	$932.91		$1,017.1967	$1,017.20	$1,017.25	$1,017.20