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	$240.54	13.817%	$273.7754	$273.78	$273.80	$273.80
Purchase #2	$120.42	9.735%	$132.1429	$132.14	$132.15	$132.10
Purchase #3	$35.52	12.145%	$39.8339	$39.83	$39.85	$39.80
Purchase #4	$63.69	6.158%	$67.612	$67.61	$67.60	$67.60
Purchase #5	$243.57	9.870%	$267.6104	$267.61	$267.60	$267.60
Purchase #6	$158.91	11.256%	$176.7969	$176.80	$176.80	$176.80
Purchase #7	$94.91	6.288%	$100.8779	$100.88	$100.90	$100.90
7 purchase totals =	$957.56		$1,058.6494	$1,058.65	$1,058.70	$1,058.60