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	$19.64	9.731%	$21.5512	$21.55	$21.55	$21.60
Purchase #2	$49.28	6.759%	$52.6108	$52.61	$52.60	$52.60
Purchase #3	$243.92	12.782%	$275.0979	$275.10	$275.10	$275.10
Purchase #4	$164.32	6.624%	$175.2046	$175.20	$175.20	$175.20
Purchase #5	$200.71	8.869%	$218.511	$218.51	$218.50	$218.50
Purchase #6	$128.42	11.524%	$143.2191	$143.22	$143.20	$143.20
Purchase #7	$242.31	6.683%	$258.5036	$258.50	$258.50	$258.50
7 purchase totals =	$1,048.60		$1,144.6982	$1,144.69	$1,144.65	$1,144.70