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	$248.82	5.528%	$262.5748	$262.57	$262.55	$262.60
Purchase #2	$38.56	9.644%	$42.2787	$42.28	$42.30	$42.30
Purchase #3	$233.36	7.606%	$251.1094	$251.11	$251.10	$251.10
Purchase #4	$25.51	13.383%	$28.924	$28.92	$28.90	$28.90
Purchase #5	$10.58	12.296%	$11.8809	$11.88	$11.90	$11.90
Purchase #6	$13.34	12.581%	$15.0183	$15.02	$15.00	$15.00
Purchase #7	$50.52	7.188%	$54.1514	$54.15	$54.15	$54.20
7 purchase totals =	$620.69		$665.9375	$665.93	$665.90	$666.00