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	$104.82	7.636%	$112.8241	$112.82	$112.80	$112.80
Purchase #2	$70.71	11.673%	$78.964	$78.96	$78.95	$79.00
Purchase #3	$117.90	4.688%	$123.4272	$123.43	$123.45	$123.40
Purchase #4	$121.66	9.793%	$133.5742	$133.57	$133.55	$133.60
Purchase #5	$63.72	6.385%	$67.7885	$67.79	$67.80	$67.80
Purchase #6	$137.81	7.796%	$148.5537	$148.55	$148.55	$148.60
Purchase #7	$243.97	6.714%	$260.3501	$260.35	$260.35	$260.40
7 purchase totals =	$860.59		$925.4818	$925.47	$925.45	$925.60