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	$127.71	3.254%	$131.8657	$131.87	$131.85	$131.90
Purchase #2	$56.60	5.220%	$59.5545	$59.55	$59.55	$59.60
Purchase #3	$234.67	5.470%	$247.5064	$247.51	$247.50	$247.50
Purchase #4	$231.41	3.855%	$240.3309	$240.33	$240.35	$240.30
Purchase #5	$12.32	10.228%	$13.5801	$13.58	$13.60	$13.60
Purchase #6	$88.41	9.848%	$97.1166	$97.12	$97.10	$97.10
Purchase #7	$47.44	12.861%	$53.5413	$53.54	$53.55	$53.50
7 purchase totals =	$798.56		$843.4955	$843.50	$843.50	$843.50