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	$64.75	11.838%	$72.4151	$72.42	$72.40	$72.40
Purchase #2	$86.80	11.798%	$97.0407	$97.04	$97.05	$97.00
Purchase #3	$47.82	5.646%	$50.5199	$50.52	$50.50	$50.50
Purchase #4	$143.51	4.653%	$150.1875	$150.19	$150.20	$150.20
Purchase #5	$58.40	6.401%	$62.1382	$62.14	$62.15	$62.10
Purchase #6	$249.86	11.829%	$279.4159	$279.42	$279.40	$279.40
Purchase #7	$137.96	5.329%	$145.3119	$145.31	$145.30	$145.30
7 purchase totals =	$789.10		$857.0292	$857.04	$857.00	$856.90