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	$18.36	5.480%	$19.3661	$19.37	$19.35	$19.40
Purchase #2	$52.43	7.136%	$56.1714	$56.17	$56.15	$56.20
Purchase #3	$187.89	13.223%	$212.7347	$212.73	$212.75	$212.70
Purchase #4	$186.38	13.277%	$211.1257	$211.13	$211.15	$211.10
Purchase #5	$78.87	9.619%	$86.4565	$86.46	$86.45	$86.50
Purchase #6	$6.69	4.760%	$7.0084	$7.01	$7.00	$7.00
Purchase #7	$36.87	10.870%	$40.8778	$40.88	$40.90	$40.90
7 purchase totals =	$567.49		$633.7406	$633.75	$633.75	$633.80