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	$30.45	3.538%	$31.5273	$31.53	$31.55	$31.50
Purchase #2	$237.36	4.641%	$248.3759	$248.38	$248.40	$248.40
Purchase #3	$42.90	12.417%	$48.2269	$48.23	$48.25	$48.20
Purchase #4	$187.60	11.129%	$208.478	$208.48	$208.50	$208.50
Purchase #5	$69.38	4.704%	$72.6436	$72.64	$72.65	$72.60
Purchase #6	$177.79	12.174%	$199.4342	$199.43	$199.45	$199.40
Purchase #7	$42.64	13.227%	$48.28	$48.28	$48.30	$48.30
7 purchase totals =	$788.12		$856.9659	$856.97	$857.10	$856.90