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	$160.93	4.496%	$168.1654	$168.17	$168.15	$168.20
Purchase #2	$221.88	8.801%	$241.4077	$241.41	$241.40	$241.40
Purchase #3	$188.66	13.781%	$214.6592	$214.66	$214.65	$214.70
Purchase #4	$32.36	11.709%	$36.149	$36.15	$36.15	$36.10
Purchase #5	$85.27	13.537%	$96.813	$96.81	$96.80	$96.80
Purchase #6	$223.44	12.444%	$251.2449	$251.24	$251.25	$251.20
Purchase #7	$70.52	11.334%	$78.5127	$78.51	$78.50	$78.50
7 purchase totals =	$983.06		$1,086.9519	$1,086.95	$1,086.90	$1,086.90