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	$86.42	3.275%	$89.2503	$89.25	$89.25	$89.30
Purchase #2	$180.35	4.477%	$188.4243	$188.42	$188.40	$188.40
Purchase #3	$27.41	8.162%	$29.6472	$29.65	$29.65	$29.60
Purchase #4	$172.91	8.832%	$188.1814	$188.18	$188.20	$188.20
Purchase #5	$218.98	3.221%	$226.0333	$226.03	$226.05	$226.00
Purchase #6	$181.40	4.670%	$189.8714	$189.87	$189.85	$189.90
Purchase #7	$38.66	4.459%	$40.3838	$40.38	$40.40	$40.40
7 purchase totals =	$906.13		$951.7917	$951.78	$951.80	$951.80