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	$218.92	5.588%	$231.1532	$231.15	$231.15	$231.20
Purchase #2	$238.49	4.841%	$250.0353	$250.04	$250.05	$250.00
Purchase #3	$54.82	4.123%	$57.0802	$57.08	$57.10	$57.10
Purchase #4	$117.88	4.821%	$123.563	$123.56	$123.55	$123.60
Purchase #5	$148.86	13.387%	$168.7879	$168.79	$168.80	$168.80
Purchase #6	$8.87	10.412%	$9.7935	$9.79	$9.80	$9.80
Purchase #7	$97.51	12.336%	$109.5388	$109.54	$109.55	$109.50
7 purchase totals =	$885.35		$949.9519	$949.95	$950.00	$950.00