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	$136.88	7.436%	$147.0584	$147.06	$147.05	$147.10
Purchase #2	$30.59	4.394%	$31.9341	$31.93	$31.95	$31.90
Purchase #3	$204.38	7.547%	$219.8046	$219.80	$219.80	$219.80
Purchase #4	$112.50	12.342%	$126.3848	$126.38	$126.40	$126.40
Purchase #5	$132.60	4.161%	$138.1175	$138.12	$138.10	$138.10
Purchase #6	$78.63	8.474%	$85.2931	$85.29	$85.30	$85.30
Purchase #7	$85.91	5.720%	$90.8241	$90.82	$90.80	$90.80
7 purchase totals =	$781.49		$839.4166	$839.40	$839.40	$839.40