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	$250.29	8.685%	$272.0277	$272.03	$272.05	$272.00
Purchase #2	$159.48	7.789%	$171.9019	$171.90	$171.90	$171.90
Purchase #3	$113.75	9.292%	$124.3197	$124.32	$124.30	$124.30
Purchase #4	$142.80	9.448%	$156.2917	$156.29	$156.30	$156.30
Purchase #5	$80.47	6.293%	$85.534	$85.53	$85.55	$85.50
Purchase #6	$14.60	8.866%	$15.8944	$15.89	$15.90	$15.90
Purchase #7	$19.96	8.302%	$21.6171	$21.62	$21.60	$21.60
7 purchase totals =	$781.35		$847.5865	$847.58	$847.60	$847.50