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	$25.26	9.760%	$27.7254	$27.73	$27.75	$27.70
Purchase #2	$250.27	12.221%	$280.8555	$280.86	$280.85	$280.90
Purchase #3	$73.90	11.646%	$82.5064	$82.51	$82.50	$82.50
Purchase #4	$147.33	11.709%	$164.5809	$164.58	$164.60	$164.60
Purchase #5	$109.47	7.550%	$117.735	$117.74	$117.75	$117.70
Purchase #6	$12.73	13.114%	$14.3994	$14.40	$14.40	$14.40
Purchase #7	$195.32	9.851%	$214.561	$214.56	$214.55	$214.60
7 purchase totals =	$814.28		$902.3636	$902.38	$902.40	$902.40