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	$36.44	9.836%	$40.0242	$40.02	$40.00	$40.00
Purchase #2	$40.40	9.508%	$44.2412	$44.24	$44.25	$44.20
Purchase #3	$46.65	13.139%	$52.7793	$52.78	$52.80	$52.80
Purchase #4	$85.70	4.347%	$89.4254	$89.43	$89.45	$89.40
Purchase #5	$84.85	6.774%	$90.5977	$90.60	$90.60	$90.60
Purchase #6	$179.91	4.729%	$188.4179	$188.42	$188.40	$188.40
Purchase #7	$234.43	8.127%	$253.4821	$253.48	$253.50	$253.50
7 purchase totals =	$708.38		$758.9678	$758.97	$759.00	$758.90