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	$16.58	9.474%	$18.1508	$18.15	$18.15	$18.20
Purchase #2	$80.88	5.845%	$85.6074	$85.61	$85.60	$85.60
Purchase #3	$95.61	8.300%	$103.5456	$103.55	$103.55	$103.50
Purchase #4	$40.31	8.416%	$43.7025	$43.70	$43.70	$43.70
Purchase #5	$162.59	7.700%	$175.1094	$175.11	$175.10	$175.10
Purchase #6	$157.66	11.703%	$176.1109	$176.11	$176.10	$176.10
Purchase #7	$217.29	11.645%	$242.5934	$242.59	$242.60	$242.60
7 purchase totals =	$770.92		$844.8200	$844.82	$844.80	$844.80