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	$53.85	11.240%	$59.9027	$59.90	$59.90	$59.90
Purchase #2	$130.67	12.747%	$147.3265	$147.33	$147.35	$147.30
Purchase #3	$59.94	11.783%	$67.0027	$67.00	$67.00	$67.00
Purchase #4	$139.59	13.294%	$158.1471	$158.15	$158.15	$158.10
Purchase #5	$91.74	3.465%	$94.9188	$94.92	$94.90	$94.90
Purchase #6	$229.49	9.457%	$251.1929	$251.19	$251.20	$251.20
Purchase #7	$184.96	6.222%	$196.4682	$196.47	$196.45	$196.50
7 purchase totals =	$890.24		$974.9589	$974.96	$974.95	$974.90