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	$250.31	12.848%	$282.4698	$282.47	$282.45	$282.50
Purchase #2	$132.50	6.123%	$140.613	$140.61	$140.60	$140.60
Purchase #3	$249.34	12.543%	$280.6147	$280.61	$280.60	$280.60
Purchase #4	$112.72	13.814%	$128.2911	$128.29	$128.30	$128.30
Purchase #5	$206.63	8.362%	$223.9084	$223.91	$223.90	$223.90
Purchase #6	$49.99	3.737%	$51.8581	$51.86	$51.85	$51.90
Purchase #7	$192.76	10.195%	$212.4119	$212.41	$212.40	$212.40
7 purchase totals =	$1,194.25		$1,320.1670	$1,320.16	$1,320.10	$1,320.20