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	$123.39	12.559%	$138.8866	$138.89	$138.90	$138.90
Purchase #2	$82.26	8.248%	$89.0448	$89.04	$89.05	$89.00
Purchase #3	$216.66	9.399%	$237.0239	$237.02	$237.00	$237.00
Purchase #4	$230.31	13.151%	$260.5981	$260.60	$260.60	$260.60
Purchase #5	$84.72	6.129%	$89.9125	$89.91	$89.90	$89.90
Purchase #6	$29.69	7.371%	$31.8784	$31.88	$31.90	$31.90
Purchase #7	$182.95	12.587%	$205.9779	$205.98	$206.00	$206.00
7 purchase totals =	$949.98		$1,053.3222	$1,053.32	$1,053.35	$1,053.30