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	$80.51	13.549%	$91.4183	$91.42	$91.40	$91.40
Purchase #2	$162.65	12.206%	$182.5031	$182.50	$182.50	$182.50
Purchase #3	$111.53	10.455%	$123.1905	$123.19	$123.20	$123.20
Purchase #4	$159.33	9.175%	$173.9485	$173.95	$173.95	$173.90
Purchase #5	$37.50	5.291%	$39.4841	$39.48	$39.50	$39.50
Purchase #6	$190.38	7.610%	$204.8679	$204.87	$204.85	$204.90
Purchase #7	$229.48	4.599%	$240.0338	$240.03	$240.05	$240.00
7 purchase totals =	$971.38		$1,055.4462	$1,055.44	$1,055.45	$1,055.40