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	$121.56	12.593%	$136.8681	$136.87	$136.85	$136.90
Purchase #2	$244.43	4.554%	$255.5613	$255.56	$255.55	$255.60
Purchase #3	$51.58	8.234%	$55.8271	$55.83	$55.85	$55.80
Purchase #4	$197.55	4.741%	$206.9158	$206.92	$206.90	$206.90
Purchase #5	$36.35	9.710%	$39.8796	$39.88	$39.90	$39.90
Purchase #6	$155.93	4.394%	$162.7816	$162.78	$162.80	$162.80
Purchase #7	$166.63	9.251%	$182.0449	$182.04	$182.05	$182.00
7 purchase totals =	$974.03		$1,039.8784	$1,039.88	$1,039.90	$1,039.90