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	$83.94	10.182%	$92.4868	$92.49	$92.50	$92.50
Purchase #2	$41.71	6.405%	$44.3815	$44.38	$44.40	$44.40
Purchase #3	$208.79	7.825%	$225.1278	$225.13	$225.15	$225.10
Purchase #4	$215.29	12.571%	$242.3541	$242.35	$242.35	$242.40
Purchase #5	$19.26	9.426%	$21.0754	$21.08	$21.10	$21.10
Purchase #6	$123.82	6.218%	$131.5191	$131.52	$131.50	$131.50
Purchase #7	$21.48	12.799%	$24.2292	$24.23	$24.25	$24.20
7 purchase totals =	$714.29		$781.1739	$781.18	$781.25	$781.20