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	$135.40	12.648%	$152.5254	$152.53	$152.55	$152.50
Purchase #2	$54.25	9.263%	$59.2752	$59.28	$59.30	$59.30
Purchase #3	$140.55	11.662%	$156.9409	$156.94	$156.95	$156.90
Purchase #4	$191.55	12.286%	$215.0838	$215.08	$215.10	$215.10
Purchase #5	$156.76	8.186%	$169.5924	$169.59	$169.60	$169.60
Purchase #6	$48.81	10.564%	$53.9663	$53.97	$53.95	$54.00
Purchase #7	$169.43	7.433%	$182.0237	$182.02	$182.00	$182.00
7 purchase totals =	$896.75		$989.4077	$989.41	$989.45	$989.40