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	$81.89	7.691%	$88.1882	$88.19	$88.20	$88.20
Purchase #2	$132.80	11.839%	$148.5222	$148.52	$148.50	$148.50
Purchase #3	$52.69	3.370%	$54.4657	$54.47	$54.45	$54.50
Purchase #4	$40.25	12.609%	$45.3251	$45.33	$45.35	$45.30
Purchase #5	$31.71	13.721%	$36.0609	$36.06	$36.05	$36.10
Purchase #6	$196.82	13.258%	$222.9144	$222.91	$222.90	$222.90
Purchase #7	$202.55	11.638%	$226.1228	$226.12	$226.10	$226.10
7 purchase totals =	$738.71		$821.5993	$821.60	$821.55	$821.60